I've searched the minimal solution possible to do PHP + WebSockets during hours, until I found this article:
Super simple PHP WebSocket example
It doesn't require any third-party library.
Here is how to do it: create a index.html containing this:
<html>
<body>
<div id="root"></div>
<script>
var host = 'ws://<<<IP_OF_YOUR_SERVER>>>:12345/websockets.php';
var socket = new WebSocket(host);
socket.onmessage = function(e) {
document.getElementById('root').innerHTML = e.data;
};
</script>
</body>
</html>
and open it in the browser, just after you have launched php websockets.php in the command-line (yes, it will be an event loop, constantly running PHP script), with this websockets.php file.