Neodymium magnets: could they damage a smartphone?

As a repair tech that has worked on phones and tablets for a number of years, I've never seen an instance where a neodymium magnet caused harm to any internal components. In fact, many phones and tablets have them built in for various reasons.

Also, it isn't necessarily the magnetic field which causes damage to sensitive components but rather the flux of the magnetic field. If you minimize the movement of the magnet with respect to the device you will minimize your chances of damaging anything.

Additionally, since the flash chips and ICs inside of modern electronics aren't magnetically-based interference isn't a problem.