Flash PHP form mailer

Hi I am VERY new to PHP, but am well versed in Flash. I am wanting to create a mailer form in Flash. I have my flash form all set up. I need help with the PHP script though. Here is the script I found on this site and it works GREAT! The only thing it is missing is a Phone Number field. With this script below where and how would I add that?

<?php

$sendTo = “senocular@hotmail.com”;
$subject = “My Flash site reply”;

$headers = “From: " . $_POST[“firstName”] .” “. $_POST[“lastname”] . “<” . $_POST[“email”] .”>
";

$headers .= "Reply-To: " . $_POST[“email”] . "
";

$headers .= "Return-path: " . $_POST[“email”];

$message = $_POST[“message”];

mail($sendTo, $subject, $message, $headers);
?>

Thanks in advance!