<?php if (!empty($_POST)): ?>
    Welcome, <?php echo htmlspecialchars($_POST["name"]); ?>!<br>
    Your email is <?php echo htmlspecialchars($_POST["email"]); ?>.<br>
<?php else: ?>
    <form action=<?php echo htmlspecialchars($_SERVER["PHP_SELF"]); ?> method="post">
        Name: <input type="text" name="name"><br>
        Email: <input type="text" name="email"><br>
        <input type="submit">
    </form>
<?php endif; ?>

Referensi

• https://stackoverflow.com/questions/5826784/how-do-i-make-a-php-form-that-submits-to-self