So I went to digital trends for the info.
While the magnets won’t destroy your phone or tablet. Magnets can cause chaos to some apps especially the ones that use the compass like map programs or any program that wants to know your location.
Also the magnets can give a magnetic charge to steel items in the phone. Which can then later on cause problems for the internal compass.
So shouild we use products like http://www.amazon.com/Universal-Magnetic-cell-phone-mount-tablet-stand-ipad-holder/dp/B014QF3D6M
It is up to you whether you use it ot not comment on if you have been using a strong magnet on your phone or tablet and either had or have not had any problems.