HTML button onClick calling JS function which calls PHP function

Question

So, my PHP functions look like that:

<?php
$guest = false;
$login = false;
$register = false;

function setGuestMode(){
    $guest = true;
    $login = false;
    $register = false;
    echo "<script>alert('Guest')</script>";
}

function setLoginMode(){
    $guest = false;
    $login = true;
    $register = false;
    echo "<script>alert('Login')</script>";
}

function setRegisterMode(){
    $guest = false;
    $login = false;
    $register = true;
    echo "<script>alert('Register')</script>";
}
?>

and my buttons who are going to call the functions look like this:

<button class="button" type="button" id="guest" onclick="colorguest(), guestLogin()">Guest Login</button>
<script type="text/javascript">function guestLogin(){"<?php setGuestMode()?>";}</script>

<button class="button" type="button" id="register" onclick="colorregister(), registerLogin()">Register</button>
<script type="text/javascript">function registerLogin(){"<?php setRegisterMode()?>";}</script>

<button class="button" type="button" id="login" onclick="colorlogin(), loginLogin()">Player Login</button>
<script type="text/javascript">function loginLogin(){"<?php setLoginMode()?>";}</script>

and my goal is to make the buttons call the php functions which are stated first. I hope someone can help me with this. Thx Fail.