I use a Garmin GPS with my phone as a backup if needed (haven't ever needed it). I use the Garmin for 2 main reasons. 1st, the screen is bigger and easier for me to see. 2nd, I would rather risk a $100 GPS falling off of the dash/windshield and getting damaged than my $600 phone. The other side note to #2 is if a crash were to occur, I'd rather have my phone in it's holder on my side where I possibly can reach it (assuming I'm awake and physically able) than potentially flying around the interior of the vehicle or out of the vehicle.
Works for me. Your mileage may vary.
