How to stay in the footer section after submit? #php - php

Question

I need a little help with PHP sessions or something similar from someone who is well versed in PHP sessions, and who has an understanding for someone who is not.
Somebody told me that it can be done with PHP sessions or that is not possible? There are some answers that can be done with Ajax but my question is - Can it be done with PHP sessions and how? Well, everything works for me - it inserts data into the database and throws out validation errors, but this is my problem: I'm doing MVC and I don't want to refresh my page after the submission so that the user has to scroll down to see validations (because I have $msg and $errors in footer), so I want the viewport to be in the same place after the submit where the messages are written - in footer. I would be very grateful if someone can see and give me a concrete answer of what I need where to put or from where what to delete. I believe the little thing is in the Controller.
P.S. Here are 1. index.php (pijaca.php) page composed of parcels, 2. pijaca-footer.php on which the form is located, 3. routes.php on which it goes from the form and 4. Controller.php.
I tried everything: putting "id" in the form and than call it from Controller - doesn't work, looked for advice and answers on the net, I probably googled something bad (it will come with time as well as experience), but I couldn't manage. Thanks in advance!
<?php
$ime = isset($ime)?$ime:"";
$prezime = isset($prezime)?$prezime:"";
$telefon = isset($telefon)?$telefon:"";
$errors = isset($errors)?$errors:[];
session_start();
?>
<?php include'pijaca-nav.php'; ?>
<?php include'pijaca-header.php'; ?>
<?php include'pijaca-about.php'; ?>
<?php include'pijaca-photo-1.php'; ?>
<?php include'pijaca-story.php'; ?>
<?php include'pijaca-photo-2.php'; ?>
<?php include'pijaca-features.php'; ?>
<?php include'pijaca-footer.php'; ?>
<footer id="contact" class="footer">
<div class="footer__box">
<form action="routes.php" id="form" class="form" method="post">
<input type="text" class="form__input" name="firstname" placeholder="First Name" value="<?php echo $ime ?>"><span>*<?php if(array_key_exists('firstname', $errors)) echo $errors['firstname'] ?></span>
<input type="text" class="form__input" name="lastname" placeholder="Last Name" value="<?php echo $prezime ?>"><span>*<?php if(array_key_exists('lastname', $errors)) echo $errors['lastname'] ?></span>
<input type="text" class="form__input" name="telephone" placeholder="Telephone No." value="<?php echo $telefon ?>"><span>*<?php if(array_key_exists('telephone', $errors)) echo $errors['telephone'] ?></span>
<button class="btn btn--green btn--form" type="submit" name="page" value="contactus">Contact us</button>
</form>
<h5 class="heading-5 heading-5--footer-box-1">
<?php if(isset($msg)) echo $msg ?>
</h5>
</div>
</footer>
<?php
require_once'../controller/Controller.php';
$controller = new Controller();
$pageGet = isset($_GET['page'])?$_GET['page']:"index";
$pagePost = isset($_POST['page'])?$_POST['page']:"index";
$page = ($pageGet != "index")?$pageGet:$pagePost;
switch ($page) {
case 'contactus':
$controller->contactus();
break;
}
<?php
require_once'../model/DAO.php';
class Controller{
public function contactus() {
$ime = isset($_POST['firstname'])?$_POST['firstname']:"";
$prezime = isset($_POST['lastname'])?$_POST['lastname']:"";
$telefon = isset($_POST['telephone'])?$_POST['telephone']:"";
$errors = [];
if (empty($ime)) {
$errors['firstname'] = "Please enter your name";
}
if (empty($prezime)) {
$errors['lastname'] = "Please enter your lastname";
}
if (empty($telefon)) {
$errors['telephone'] = "Please enter your telephone";
} else {
if (preg_match('/^[0-9 +_-]*$/', $telefon)) {
} else {
$errors['telephone'] = "Please enter a number";
}
}
if (count($errors) == 0) {
$dao = new DAO();
$podacikorisnika = $dao->korisnik($ime, $prezime, $telefon);
$msg = "Sucsses!";
include 'pijaca.php';
} else {
$msg = "Please enter all fileds";
include 'pijaca.php';
}
}
}