There shouldn't be anything in the faceplate that cares about magnets. But if you want to be certain, take a magnet from a scrapped hard drive (strong and free) or a good refrigerator magnet (inexpensive) and try running it around the faceplate to make sure nothing happens.
Magnetic phone mounts can be a bad idea. If you are ever in a crash, the phone becomes a missile. (as does everything that's not secured.) Even if it doesn't hit you, it may be smashed, lost, and useless if you need it to call for help. FWIW.