$curl = curl_init();

curl_setopt_array($curl, array(
    CURLOPT_URL => 'https://smsv3.mensajesms.com.ve/api/v1/sendsms',
    CURLOPT_RETURNTRANSFER => true,
    CURLOPT_ENCODING => '',
    CURLOPT_MAXREDIRS => 10,
    CURLOPT_TIMEOUT => 0,
    CURLOPT_FOLLOWLOCATION => true,
    CURLOPT_HTTP_VERSION => CURL_HTTP_VERSION_1_1,
    CURLOPT_CUSTOMREQUEST => 'POST',
    CURLOPT_POSTFIELDS => array('token' => env('KEY_SMS'),'user' => env('USER_SMS'),'celular' => $phone,'mensaje' => $msg),
));
$response = curl_exec($curl);

curl_close($curl);