WebRTC in general does not appreciate page reloading. When a page is reloaded, it loses all its previous resources (media streams and peer connections). If you are doing the usual PHP thing of "reload the entire page every time something trivial happens", then forget about using WebRTC.
If you are aren't reloading the entire page, then you can probably run NodeJs along side your PHP server. There is a document all about doing that. See
https://easyrtc.com/docs/easyrtc_with_other_servers.php .
If you want something that stays in the PHP world, look for a webrtc toolkit based on PHP. I don't know if there is one but WebRTC has been around for a few years now, so you'd expect somebody to have written one.