How to get isset() to execute MORE than once in PHP? [duplicate]

I’m trying to do something that should be simple. I want a button that every time it’s clicked to update an mysql row value to increment by 1. so click in ten times and the value is 10. I am trying to use isset() to do this, with just normal variables to test:

php:

   $amount = 0;

   if(isset($_POST['button1'])) {
   echo "button 1 clicked";
   $amount++;
   }

html:

<form method="post">
    <input class="button" type="submit" value="select" name="button1"></input>
</form>

<h1><?= $amount ?></h1>

this works, but only once. My thought was that since $_POST[‘button1’] is now set, it doesn’t execute again because it is only supposed to execute when the value is no longer null and that only happens once. so, I thought I’d try:

   unset($_POST[‘button1’]);

in the isset() block, or even:

   $_POST[‘button1’] = null;

so that the button click would hopefully redefine it, but no luck. what do I do? most questions want a button to click only once, but I want the opposite, for it to theoretically click forever. why can’t a button just call a function like in js? I know php probably isn’t the best choice for this kind of project, but is there a way?