I am fairly new to PHP (about 8 months). I am building a web app, which is almost ready for beta. I am only now starting to think about what I would need to do to make a mob
NO, YOU DON'T NEED ANY FRAMEWORK FOR PHP BACKEND.
If you are using php as backend then you don't need to use any resetAPI framework. Just create you own php files and generate JSON output for each response.
You must generate JSON output. That is enough. Benefits:- If you use own login to generate Json output then it will be tremendous light speed (based on your logic). If you use any framework then the performance issues will occure.
It will be better if you can design your own mini framework to do specific site's work.
Thanks