I have an S6 i want to tank mount for the GPS function....
You can do what you want but here is something to think about.
I use a GPS unit on my bike and keep my cell phone on me via a clip on my belt.
If you are ever in an accident and become separated from your bike (which is a strong possibility) and your phone is on your bike you
will not be able to call for help. This is most probable in an accident where no one else is around and maybe you took a curve to fast or
a critter jumped out in front of you or oil on the road and you slid off the road and over a hill/cliff etc. Especially if you were not able to walk back to your bike
because of injuries from the crash. Not to mention if you hit something solid your phone might very well leave the bike and you can't find it.
By keep your phone on you, your chances of calling for help are greatly improved. JMO.