I have a Surface Duo phone. Using both screens together is like using a tablet, but it folds up and fits in my pocket. I can have the keyboard on one screen and have a full display on the other. I can look something up on one screen while using something else on the other screen.

By comparison, the standard of "splitting" a single screen results in something that is often too small and awkward to use and with too little screen space for comfortable viewing.