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.
Everything that is not secured can become a secondary projectile in an MVA , don't worry about it breaking , worry about it breaking You! I have been to PIAA'S where drivers were killed by the old bagphone cellular phones and other things like a a temporary stereo, Maglite flashlight s ,all very normal to be in a car environment but not properly stowed and secured.