As long as cellular service is working, it should be OK. If cellular service is interrupted, you scanner phone app may not work at all. With a real scanner, you by-pass this issue.
You still want a working cell phone for one very important reason. And as long as you have it, you might as well take advantage of the feature while it's available.
Oh, the reason. It tells you whether or not the cell system is working, or has been killed by EMP, solar flare, or shut down. In which case, things just got a notch worse than routine.