demo/assets/php/reg.php

<?php

if(!empty($_POST['reg'])){
    $sql = 'INSERT INTO `users`(`fullname`, `email`, `login`,
    `password`,`phone`) VALUES (:fullname,:email,:login,:password,:phone)';
    $sth = $dbh->prepare($sql, [PDO::ATTR_CURSOR => PDO::CURSOR_FWDONLY]);
    $sth->execute([
        "fullname"=>$_POST['fullname'],
        "email"=>$_POST['email'],
        "login"=>$_POST['login'],
        "password"=>$_POST['password'],
        "phone"=>$_POST['phone']
    ]);
    header('Location: login.php');
}
?>