Untitled

How can I modfy this send.php $mail call to include the $phone paramerter
$post = (!empty($_POST)) ? true : false;

if($post)
{
    $name    = stripslashes($_POST['name']);
    $email   = trim($_POST['email']);
    $phone   = trim($_POST['phone']);
    $subject = trim($_POST['subject']);
    $message = stripslashes($_POST['message']);

    $error = '';

    // Check name
    if(!$name)
        $error .= 'Name required! ';

    // Check email
    if(!$email)
        $error .= 'E-mail required! ';

    if($email && !ValidateEmail($email))
        $error .= 'E-mail address is not valid! ';

    // Check phone
    if(!$phone)
        $error .= 'Phone number required! ';


    // Check message
    if(!$message)
        $error .= "Please enter your message!";

    if(!$error)
    {
        $mail = mail(WEBMASTER_EMAIL, $subject, $message,
             "From: ".$name." <".$email.">rn"
            ."Reply-To: ".$email."rn"
            ."X-Mailer: PHP/" . phpversion());

        if($mail)
            echo 'OK';
    }
    else
        echo '<div class="errormsg">'.$error.'</div>';
}

$message = "Phone: $phonern" . $message;

$mail = mail(WEBMASTER_EMAIL, $subject, $message,
         "From: ".$name." <".$email.">rn"
        ."Reply-To: ".$email."rn"
        ."X-Mailer: PHP/" . phpversion());