I have a garmen 1030 plus and love it. I also use my phone mount sometimes. The garmen is great for pre planned routes, integrated maps with all the bike functions. I can
flip through screen while on the go. It's awesome. Sometimes after you have already been riding a while and want to go some where else nothings beats a modern phone and google/apple maps. You can zoom in/out so fast on the phone. pick an intersection to go back or just search for something. Maybe you parked by sportsbasement etc...
You're in bike group and someone got a flat. They can send you a pin drop and you can go back and help them.
I would never use phone 100% of the time. Kills batteries too fast. Is not integrated with bike functions and gps/map etc...