<?php
$a= $_POST['a'];
$b= $_POST['b'];
$c= $_POST['c'];
echo ПХП ОТКРЫЛСЯ И РАБОАТЕТ";
echo $a;
echo $b;
echo $c;
?>

///////////////////////////////////////////////////////////////////

<html>
<head>
<script src="/js/jquery-3.1.1.min"></script>

<script>
function init() {
var first = 1;
var second = 2;
var third = 3;
$.post('my.php',{"a":first,"b":second,"c":third});
};
</script>

</head>
<body>
		<a onClick="init()" href="my.php">Button</a>
</body>
</html>