如何修改此send.php$mail调用以包含$phone参数

如何将我添加的电话号码参数获取到此php脚本发送的电子邮件正文中？：

$post = (!empty($_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." <".$email.">'r'n"
            ."Reply-To: ".$email."'r'n"
            ."X-Mailer: PHP/" . phpversion());
        if($mail)
            echo 'OK';
    }
    else
        echo '<div class="errormsg">'.$error.'</div>';
}

我已经在$post部分添加了$phone，在我的表单中创建了feild，现在我只需要在收到的电子邮件中返回内容。非常感谢任何提示。