SendExmpl.php

<?php

$phoneNumbers = [
    'phone1',
    'phone2',
];

$params = [
    'user'     => 'user',
    'password' => 'password',
    'msisdn'   => implode(',', $phoneNumbers),
    'sid'      => 1,
    'msg'      => 'test',
    'fl'       => 0,
    'gwid'     => 123
];

$apiURL      = 'http://sms.vndsms.com/vendorsms/pushsms.aspx';
$paramsQuery = http_build_query($params);
$fullURL     = sprintf('%s?%s', $apiURL, $paramsQuery);

$response = json_decode(file_get_contents($fullURL), true);