When I change my php contact form to happen to post, it does not work

Here is my contact form and you can see it here at benlevywebdesign.com at the bottom of the page.

<form id="form1" action="<?php echo $_SERVER['PHP_SELF']; ?>" enctype="text/plain" method="get">    

        <fieldset>
            <p class="form">
                <label for="name">Name</label>
                <input type="text" name="name" id="name" size="30" />
            </p>
            <p class="form">
                <label for="email">Email</label>
                <input type="text" name="email" id="email" size="30" />
            </p>
            <p class="form">
                <label for="web">Website</label>
                <input type="text" name="web" id="web" size="30" />
            </p>
        </fieldset>
        <fieldset>
            <p class="form">
                <label for="message">Message</label>
                <textarea name="message" id="message" cols="30" rows="10"></textarea>
            </p>
        </fieldset>                 

        <p class="submit"><button name="submit" type="submit">Send</button></p>

    </form>`

and here is the php code I am trying to switch from get to post. I don't know that much php

<?php
        if(isset($_GET['submit'])){

            $to = "benlevygraphics@gmail.com";
            $headers = "From: " . $_GET['email'];
            $subject = "Ben, you have been contacted by...";
            $body = "Name: " . $_GET['name'] . "\nEmail: " . $_GET['email'] . "\nWebsite: " . $_GET['web'] . "\nMessage: " . $_GET['message'];
            if(mail($to, $subject, $body, $headers)){
                echo("<p>Your message has been sent!</p>");
            }
            else{
               echo("<p>Message delivery failed...</p>");
            }
       }

?>

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First, get rid of your enctype attribute. You are setting it to text/plain about which the specification says:

Payloads using the text/plain format are intended to be human readable. They are not reliably interpretable by computer

Second, set method to "POST"

Third, in the PHP use $_POST not $_GET

Fourth, don't output content from $_POST/GET/SERVER/ETC into an HTML document without first encoding it with htmlspecialchars. Otherwise you have a huge XSS security vulnerability.