You can't do that, PHP is a server-side language, that means it renders when the page loads and not after that.
The solution can be to call a PHP via AJAX, that PHP can have the case conditions and then it will render what you want.
Example:
The javascript (using jQuery):
$(".yourbutton").click(function(event){
event.preventDefault();
$.post("yourPHP.php", {var: somethingdynamicpassedviajavascript},
function(data){
//get ther result
$("#yourdiv").html(data);
}, "html");
});
What this does is place a click event into something with a class named "yourbutton", and when you click that, it will call an external PHP via an AJAX post, sending a var (in this example), you can send something dynamic, change the "somethingdiynamicpassedviajavascript" with some var.
PHP (yourPHP.php):
$myvar = $_REQUEST['var'];
//do your cases here:
switch ($myvar) {
case "1":
echo "this is for the case 0";
break;
case 1:
echo "this is for the case 1";
break;
}
Here you get that var, and depending on the case, send a different output.
Notice that this may need to add a test for POST and other anti-vandalism methods...
if(something == $php_variable) then ($php_variable_that_tells_js_to_do_something). The javascript will NOT run the php code, all php code will run before the JS.