I used to have a mount made from a otterbox case with a ram ball epoxied to the back. When I got a new phone, I decided I didnt want an otterbox anymore and someone here (sorry, I dont remember who, but thank you) pointed to this option
https://www.quadlockcase.ca/ and I have went to it. I like it so far. I got a dedicated case for my phone and a universal adapter and epoxied it to the case of an inexpensive 7" samsung tablet which will serve as my GPS on my bike. Just got it a couple of months back so I have to wait till spring to try it on the bike but it works good in my truck.
EDIT: sorry, forgot to mention, My Tablet then sits on a ram ball in the center of the handlebar riser along with a powerlet plug to power it