There is wp-discourse
But that is a WordPress plugin not a Discourse plugin.
As I posted earlier, I have yet to see any Discourse plugins written in PHP
I can understand that PHP devs might not want to touch Ruby, but Ruby is the language of Discourse.
Well, that and Ember
If the devs don’t want to get into Ruby they might be able to get somewhere (albeit likely only to limited extent) working with Ember alone.
But AFAIK, preferred language or otherwise, there is no PHP in Discourse