So, you simply need to add an optional large screen, keyboard, and mouse to your phone. It has already been done. Now it just needs to be done a little better?
See also: Microsoft Continuum, Motorola Atrix (probably the first Android that turned into a laptop)
Yay, and with Emui and DeX growing up, it seems to be next revolution about smartphones replacing your PC's. For instance, the Mirabook from Miraxess : https://miraxess.com/samsung-note-8-laptop/
What makes a laptop a laptop is a decent keyboard and a reasonably large screen. There is a fundamental mismatch between the screen size comfortable for the eyes, keyboard size comfortable for typing, and device size comfortable for holding in hand. Because of this, I don't think phones and laptops will ever converge; tablets and laptops are already actively converging, though.