Imo, a phone can work very well as a bike computer. It wont have the endless (mostly useless?) functions as a dedicated computer usually has, but the processor is much faster, the screen is bigger and has better resolution and its connected to the internet so no additional up or downloading of routes and data. This means quick route planning directly on the device, on the fly rerouting and routes planned in say Komoot on a PC is "just there" when you open the Komoot app on the phone. Of course it doesn't work well if you keep it in the pocket or you ride epic rides and don't bring a small power brick.