i just installed a generic quad lock and it's super easy to mount and i would certainly not call it pricey.

i don't use my phone on the bike much but researched for awhile between the two options - having a dedicated garmin-like unit and just using my phone. fyi it is possible to use offline maps with some phone mapping programs such as one of the best - google maps. you can pre-select areas on the map to load for offline use.

i like google maps because it has dedicated bicycle directions that take into account local bike infrastructure. and since it's google maps, they are updated constantly and for free. the main reason i don't like the phone is because it chews through battery. and while i usually carry around a 10,000 mah batter with me on longer rides, it's a pain to charge the phone while riding - easy enough when stopped.

i have not used my phone enough to conclude whether the shaking and rattling is affecting it. on the flip side i have yet to find a post or article where someone says their phone was damaged by using it on a bike.