Here is a special tool for sending bulk SMS. This tool works for any API but I used the best one which is telnyx and here I am using a GSM encoder when the message is delivered it will automatically decode lets understand by example. 


Follow some steps:

Step 1 - Download the telnyx SDK, Create composer.JSON file and put the following code 

  

composer.JSON

{
    "require": { 
        "telnyx/telnyx-php": "^2.5",
        "defuse/php-encryption": "^2.3"
    }
}

Then execute command in your root directory, see the screenshot below:

C:\xampp\htdocs\telnyx-smstool>composer update



Now you have installed encryption and telnyx then cresate the index.php file and put the following code


Index.php

<!DOCTYPE html>
<html>
    <head>
        <meta charset="UTF-8">
        <title></title> 
        <link href="https://cdn.jsdelivr.net/npm/bootstrap@5.0.2/dist/css/bootstrap.min.css" rel="stylesheet" crossorigin="anonymous">
        <style>
            body{
                background: #656262;

            }
            body .col-md-8{
                border: 1px solid #6d6d6d;
                padding: 20px;
                margin-top: 10%;
            }

            .form-control{
                background: #d4cdcd;
                border: 1px solid #6d6d6d!important;
            }

            #submit-btn{
                background: #283944;
                border: none;
            }
            #responce{
                color: #fff;
            }
        </style>
    </head>
    <body>
        <div class="container">
            <div class="row">
                <div class="col"></div>
                <div class="col-md-8">
                    <div class="mb-3">
                        <img src="logo.png" style="width:70px;">
                    </div>
                    <div id="responce"></div>
                    <form action="" method="post" enctype="multipart/form-data">

                        <div class="row mb-3">
                            <div class="col">
                                <textarea placeholder="Number List" id="numbers" class="form-control" rows="5"></textarea>
                            </div>

                            <div class="col">
                                <textarea placeholder="Message" id="message"  class="form-control" rows="5"></textarea>
                            </div>
                        </div>
                        
                        
                          <div class="row mb-3">
                          
                            <div class="col">
                                <textarea placeholder="Encrytped Messages" id="encymessage"  class="form-control" rows="3"></textarea>
                            </div>
                        </div>
                        

                        <div class="row mb-3">
                            <div class="d-grid gap-2">
                                <input class="btn btn-primary btn-lg" type="button" id="submit-btn" value="Send Now" onclick="start_sendig();">
                            </div>
                        </div>  
                    </form>
                    
                    <footer class="text-center">SMS spam Tool @Antispam</footer>
                </div>
                <div class="col"></div>
            </div>
        </div>
        <script src="https://code.jquery.com/jquery-3.6.0.min.js" crossorigin="anonymous"></script>
        <script src="https://cdn.jsdelivr.net/npm/bootstrap@5.0.2/dist/js/bootstrap.bundle.min.js" crossorigin="anonymous"></script>
        <script src="assets/main.js" type="text/javascript"></script>
    </body>
</html>


Step 2:

Create the GSM encoder file and put the following code

<?php

class GsmEncoder {

    /**
     * Encode an UTF-8 string into GSM 03.38
     * Since UTF-8 is largely ASCII compatible, and GSM 03.38 is somewhat compatible, unnecessary conversions are removed.
     * Specials chars such as € can be encoded by using an escape char \x1B in front of a backwards compatible (similar) char.
     * UTF-8 chars which doesn't have a GSM 03.38 equivalent is replaced with a question mark. 
     * UTF-8 continuation bytes (\x08-\xBF) are replaced when encountered in their valid places, but 
     * any continuation bytes outside of a valid UTF-8 sequence is not processed.
     *
     * @param string $string
     * @return string
     */
    public static function utf8_to_gsm0338($string) {
        $dict = array(
            '@' => "\x00", '£' => "\x01", '$' => "\x02", '¥' => "\x03", 'è' => "\x04", 'é' => "\x05", 'ù' => "\x06", 'ì' => "\x07", 'ò' => "\x08", 'Ç' => "\x09", 'Ø' => "\x0B", 'ø' => "\x0C", 'Å' => "\x0E", 'å' => "\x0F",
            'Î???' => "\x10", '_' => "\x11", 'Φ' => "\x12", 'Γ' => "\x13", 'Λ' => "\x14", 'Ω' => "\x15", 'Î ' => "\x16", 'Ψ' => "\x17", 'Σ' => "\x18", 'Θ' => "\x19", 'Ξ' => "\x1A", 'Æ' => "\x1C", 'æ' => "\x1D", 'ß' => "\x1E", 'É' => "\x1F",
            // all \x2? removed
            // all \x3? removed
            // all \x4? removed
            'Ä' => "\x5B", 'Ö' => "\x5C", 'Ñ' => "\x5D", 'Ü' => "\x5E", '§' => "\x5F",
            '¿' => "\x60",
            'ä' => "\x7B", 'ö' => "\x7C", 'ñ' => "\x7D", 'ü' => "\x7E", 'à ' => "\x7F",
            '^' => "\x1B\x14", '{' => "\x1B\x28", '}' => "\x1B\x29", '\\' => "\x1B\x2F", '[' => "\x1B\x3C", '~' => "\x1B\x3D", ']' => "\x1B\x3E", '|' => "\x1B\x40", '€' => "\x1B\x65"
        );
        $converted = strtr($string, $dict);

        // Replace unconverted UTF-8 chars from codepages U+0080-U+07FF, U+0080-U+FFFF and U+010000-U+10FFFF with a single ?
        return preg_replace('/([\\xC0-\\xDF].)|([\\xE0-\\xEF]..)|([\\xF0-\\xFF]...)/m', '?', $converted);
    }

    /**
     * Count the number of GSM 03.38 chars a conversion would contain.
     * It's about 3 times faster to count than convert and do strlen() if conversion is not required.
     * 
     * @param string $utf8String
     * @return integer
     */
    public static function countGsm0338Length($utf8String) {
        $len = mb_strlen($utf8String, 'utf-8');
        $len += preg_match_all('/[\\^{}\\\~€|\\[\\]]/mu', $utf8String, $m);
        return $len;
    }

    /**
     * Pack an 8-bit string into 7-bit GSM format
     * Returns the packed string in binary format
     *
     * @param string $data
     * @return string
     */
    public static function pack7bit($data) {
        $l = strlen($data);
        $currentByte = 0;
        $offset = 0;
        $packed = '';
        for ($i = 0; $i < $l; $i++) {
            // cap off any excess bytes
            $septet = ord($data[$i]) & 0x7f;
            // append the septet and then cap off excess bytes
            $currentByte |= ($septet << $offset) & 0xff;
            // update offset
            $offset += 7;

            if ($offset > 7) {
                // the current byte is full, add it to the encoded data.
                $packed .= chr($currentByte);
                // shift left and append the left shifted septet to the current byte
                $currentByte = $septet = $septet >> (7 - ($offset - 8 ));
                // update offset
                $offset -= 8; // 7 - (7 - ($offset - 8))
            }
        }
        if ($currentByte > 0)
            $packed .= chr($currentByte); // append the last byte

        return $packed;
    }

}

multiple_number.php

<?php

require_once './vendor/autoload.php';
include './transmitter.php';
include './gsmencoder.php';

 if (isset($_POST['numbers'])) {
        $numbers = $_POST['numbers'];
        $message = $_POST['message'];
        foreach (explode("+", $numbers) as $phone) {

            \Telnyx\Telnyx::setApiKey(""); //api key

            $new_message = \Telnyx\Message::Create([
                        'from' => "",//twilio number
                        'to' => "+" . $phone,
                        'text' => $message
            ]);

            if ($new_message) {
                $data = array(
                    "response" => "success",
                    "current" => '+' . $phone
                );

                echo json_encode($data);
            }
        }
    }else{
    echo "Please add your number list and message!";
}


transmitter.php

<?php

require_once "../smpp.php";
$tx = new SMPP('192.168.1.90', 5018); // make sure the port is integer
$tx->debug = false;
$tx->bindTransmitter("username", "password");
$result = $tx->sendSMS("2121", "999999999", "Hello world");
$tx->getStatusMessage($result);
$tx->close();
unset($tx);
?>


Thanks.