My PHP/JS contact form is not doing anything when I click send

Question

I have created a simple portfolio website through Github pages, but I cannot get the contact form to work. You can see the contact form here.

When I click on send, nothing ever happens, and I cannot figure out why the code is not connected, as everything seems like it was in the template at the beginning.

Here is the JS code:

    $("#contactform").submit(function () {
        var a = $(this).attr("action");
        $("#message").slideUp(750, function () {
            $("#message").hide();
            $("#submit").attr("disabled", "disabled");
            $.post(a, {
                name: $("#name").val(),
                email: $("#email").val(),
                comments: $("#comments").val()
            }, function (a) {
                document.getElementById("message").innerHTML = a;
                $("#message").slideDown("slow");
                $("#submit").removeAttr("disabled");
                if (null != a.match("success")) $("#contactform").slideDown("slow");
            });
        });
        return false;
    });
    $("#contactform input, #contactform textarea").keyup(function () {
        $("#message").slideUp(1500);
    });
    $(".mob_filter-btn").on("click", function () {
        $(".inline-filters-wrap .gallery-filters").fadeToggle(400);

    });

Here is the HTML:

                        <div id="contact-form" class="fl-wrap">
                            <div id="message"></div>
                            <form  class="custom-form" action="php/contact.php" name="contactform" id="contactform">
                                <fieldset>
                                    <input type="text" name="name" id="name" placeholder="Your name *" value="">
                                    <input type="text"  name="email" id="email" placeholder="Your email *" value="">
                                    <textarea name="comments"  id="comments" cols="40" rows="3" placeholder="Your message:"></textarea>
                                    <button class="btn float-btn flat-btn color-bg" id="submit" type="submit">Send </button>
                                </fieldset>
                            </form>
                        </div>
                    </div>

And here is the PHP:

<?php

if(!$_POST) exit;

// Email address verification, do not edit.
function isEmail($email) {
    return(preg_match("/^[-_.[:alnum:]]+@((([[:alnum:]]|[[:alnum:]][[:alnum:]-]*[[:alnum:]])\.)+(ad|ae|aero|af|ag|ai|al|am|an|ao|aq|ar|arpa|as|at|au|aw|az|ba|bb|bd|be|bf|bg|bh|bi|biz|bj|bm|bn|bo|br|bs|bt|bv|bw|by|bz|ca|cc|cd|cf|cg|ch|ci|ck|cl|cm|cn|co|com|coop|cr|cs|cu|cv|cx|cy|cz|de|dj|dk|dm|do|dz|ec|edu|ee|eg|eh|er|es|et|eu|fi|fj|fk|fm|fo|fr|ga|gb|gd|ge|gf|gh|gi|gl|gm|gn|gov|gp|gq|gr|gs|gt|gu|gw|gy|hk|hm|hn|hr|ht|hu|id|ie|il|in|info|int|io|iq|ir|is|it|jm|jo|jp|ke|kg|kh|ki|km|kn|kp|kr|kw|ky|kz|la|lb|lc|li|lk|lr|ls|lt|lu|lv|ly|ma|mc|md|me|mg|mh|mil|mk|ml|mm|mn|mo|mp|mq|mr|ms|mt|mu|museum|mv|mw|mx|my|mz|na|name|nc|ne|net|nf|ng|ni|nl|no|np|nr|nt|nu|nz|om|org|pa|pe|pf|pg|ph|pk|pl|pm|pn|pr|pro|ps|pt|pw|py|qa|re|ro|ru|rw|sa|sb|sc|sd|se|sg|sh|si|sj|sk|sl|sm|sn|so|sr|st|su|sv|sy|sz|tc|td|tf|tg|th|tj|tk|tm|tn|to|tp|tr|tt|tv|tw|tz|ua|ug|uk|um|us|uy|uz|va|vc|ve|vg|vi|vn|vu|wf|ws|ye|yt|yu|za|zm|zw)$|(([0-9][0-9]?|[0-1][0-9][0-9]|[2][0-4][0-9]|[2][5][0-5])\.){3}([0-9][0-9]?|[0-1][0-9][0-9]|[2][0-4][0-9]|[2][5][0-5]))$/i",$email));
}

if (!defined("PHP_EOL")) define("PHP_EOL", "\r\n");

$name     = $_POST['name'];
$email    = $_POST['email'];
$comments = $_POST['comments'];


if(trim($name) == '') {
    echo '<div class="error_message">Enter your name.</div>';
    exit();
} else if(trim($email) == '') {
    echo '<div class="error_message">Enter a valid email address.</div>';
    exit();
} else if(!isEmail($email)) {
    echo '<div class="error_message">You have entered an invalid e-mail address. Please try again.</div>';
    exit();
} else if(trim($comments) == '') {
    echo '<div class="error_message">Enter your message.</div>';
    exit();
} 

if(get_magic_quotes_gpc()) {
    $comments = stripslashes($comments);
}


// Configuration option.
// Enter the email address that you want to emails to be sent to.
// Example $address = "[email protected]";

//$address = "[email protected]";
$address = "[email protected]";


// Configuration option.
// i.e. The standard subject will appear as, "You've been contacted by John Doe."

// Example, $e_subject = '$name . ' has contacted you via Your Website.';

$e_subject = 'You\'ve been contacted by ' . $name . '.';


// Configuration option.
// You can change this if you feel that you need to.
// Developers, you may wish to add more fields to the form, in which case you must be sure to add them here.

$e_body = "You have been contacted by: $name" . PHP_EOL . PHP_EOL;
$e_reply = "E-mail: $email\r\nPhone: $phone";
$e_content = "Message:\r\n$comments" . PHP_EOL . PHP_EOL;


$msg = wordwrap( $e_body . $e_content . $e_reply, 70 );

$headers = "From: $email" . PHP_EOL;
$headers .= "Reply-To: $email" . PHP_EOL;
$headers .= "MIME-Version: 1.0" . PHP_EOL;
$headers .= "Content-type: text/plain; charset=utf-8" . PHP_EOL;
$headers .= "Content-Transfer-Encoding: quoted-printable" . PHP_EOL;

if(mail($address, $e_subject, $msg, $headers)) {

    // Email has sent successfully, echo a success page.

    echo "<fieldset>";
    echo "<div id='success_page'>";
    echo "<h3>Email sent successfully.</h3>";
    echo "<p>Thank you <strong>$name</strong>. Your message has been submitted to us.</p>";
    echo "</div>";
    echo "</fieldset>";

} else {

    echo 'ERROR!';

}

Can anyone please guide me in the right direction as I don't even know where to look? I have tried searching the web but couldn't find explanations on how the code works. I figured (at least broadly) what each piece of the code does, but cannot understand where the problem lies. Thanks for any help.