It can be pretty frustrating when dealing with old code bases. However its introducing a lot of really great features, so if you've got the time to either start a new project or rewrite with the more modern features you'll be fine.

For what I remember, it was just a normal interpreted language but you had to put "$" everywhere.

The literal entirety of Facebook / Instagram / Whatsapp's backend is built on PHP.

I'm not saying that was a good choice, but it does guarantee a lot of resources flowing to it's development.