PHP is a standalone, famous and widely using programming language to build server side applications. NodeJs is a javascript run-time which allows to run javascript as a server side language.
But when you come to back-end development there are lot of architecture scenarios, that you should consider about.
Use PHP,
- If you are using monolithic architecture.
- For standalone applications
Use NodeJS
- For API end points
- Cloud Native Functions
- Micro Service Architecture
I recommend you to learn nodejs for your future career!