It was definitely a thing for awhile. IIRC Mozilla made a phone OS that could do this and I think Ubuntu too. I think those projects gave up too quickly. Sometimes things take time and idk why in CS we have to always be in a rush. If Goodyear, who's made tires for 100 years, can take 8 years to make a tire, I think we can take that time to make a new novel OS that has a phone mode and desktop mode. Certainly such a thing is going to take time for people to even wrap their heads around