Both use the underlying stack:
gnome-session, g-c-c, network and modem manager, etc.
And both follow the gnome design patterns for mobile.
But the shell's themselves, gnome-shell and phosh are different, phosh is written in gtk and gnome-shell is not.
So sharing code between the two shells is hard.
Got Mobian (almost) ported to Pixel 3a / 3a XL (lemmy.sdf.org)
Most parts work, still not sure why Bluetooth gives me errors in dmesg, audio out works, microphone input not yet… I’m getting there....