They already exist.

In the Android world we have DeGoogled OSes like LineageOS, GrapheneOS, and /e/OS.

In the Linux phone world we have Mobian (Mobile Debian), Mobile Plasma, etc.. Linux phones work much better than people give them credit for. Linux phones do "convergence" better then any other phones. Convergence is when you use your phone as a phone, and you also dock it to a keyboard, mouse and monitor, and use it as your computer.