RM500 camera secondhand is definitely better than an RM500 phone camera. It is even better than a mid ranger.

The picture will be much sharper and less auto focus issue. Cameras have much better quality sensors and lenses. The only question is, when you go out, will you bring camera with you all the time? I am sure you will remember to bring your phone. Camera, after a while you will be lazy to bring it out everytime unless there is an event.