- only works with very few phone models
- battery doesn’t last long
- bad UI with tiny elements.
- not managing a smooth refresh rate
- no apps
That‘s the pattern we‘ve seen over and over again. The only approach that has worked better is to base things on AOSP.
In AOSP, not even the call app is usable nowadays. AOSP doesn't have any functional UI anymore.
So depends what's your definition of a phone stack, if it includes a call app, an agenda or a keyboard, AOSP doesn't fit it.
If I were to do a Linux Phone platform, I'd be targeting feature phone levels of functionality to begin with, with a focus on battery life and actually working telephony. I'd be aggressively throwing Wayland/GTK and all that nonsense in the bin just to get something basic working well. Draw straight to the framebuffer if you have to. This doesn't help with the app problem, but it sets a tide mark for quality & performance, and it can be iterated on.
That said, if you want to start without the entire Linux desktop stack, you can, and there's even a project that already does something like that IIUC: https://sr.ht/~mil/framebufferphone/