contact-form.php

<?php
    // only run this code if they submitted the form (we can check if the submit button was pressed)
    if (isset($_POST['contact-submit'])) {

        $email = isset($_POST['email']) ? trim($_POST['email']) : '';
        $name = isset($_POST['name']) ? trim($_POST['name']) : '';
        $message = isset($_POST['message']) ? trim($_POST['message']) : '';

        success = true;

        // validate email
        if ($email == '') {
            // TODO: handle 'missing email' error

            success = false;
        } elseif (!preg_match('/^[^@]+@[^@]+$/', $email)) {
            // TODO: handle 'this doesnt look like an email' error

            success = false;
        }

        // do similar for name and message

        if (success) {
            mail('info@taxifriend.com', 'Incoming Transmission', "From $name, $email, $phone:\r\n----------------------\r\n$message");

            ?>
            <p><strong>Thank you!</strong>  Your message has been sent.</p>
            <?php

            // redirect to self so that pressing "refresh" doesn't re-submit form data
            $SELFPAGE = $_SERVER['PHP_SELF']; 
            header("location: $SELFPAGE");
            exit;
        } else {
            ?>
            <p><strong>Uh oh.</strong> Please make sure all fields are filled out and that the information is correct.</p>
            <?php
        }

    }
?>
<form method="POST" action="">
    <div>
        <label for="contact-email">Email</label>
        <input id="contact-email" type="email" name="email" value="<?php echo $email; ?>" placeholder="you@example.com">
    </div>
    <div>
        <label for="contact-name">Name</label>
        <input id="contact-name" type="text" name="name" value="<?php echo $name; ?>" placeholder="John Smith">
    </div>
    <div>
        <label for="contact-message">Message</label>
        <textarea id="contact-message" name="message" placeholder="Type a message... (optional)"><?php echo $message; ?></textarea>
    </div>
    <div>
        <input type="submit" name="contact-submit" value="Please Contact Me">
    </div>
</form>