I would think that would already exist if it was actually compelling.
But having to plug your computing device into a monitor and keyboard to do any work is just a downgrade from a laptop that always has a monitor and keyboard. It's a bizarre portability trade-off that's even less exciting as laptops become thinner, lighter, and more powerful.
I do this with my Samsung note 10. Also when I plug my Samsung tablet into my usb-c monitor I get a nice desktop. Lastly, purism’s phone supports phone-as-desktop as well