Makes me think of Ubuntu Unity. I wish that vision became a reality. A secure, open source OS on a phone that is adaptable to other form factors. That would be amazing!
Discussion
I am writing this from waydroid on Ubuntu Touch. Ubuntu touch probably is the most fleshed out can plug into monitor with fairphone 4 works decently. PostmarketOs is further behind but I like it more with the mobile gestures and set up way better than Ubuntu Touch. Both not the easiest thing to daily drive unfortunately. We can dream for now.
Purism has already created the convergence Linux phone with their Librem5 and Liberty phones.
They also have a lapdock that you can buy for the setup.