It takes up about ⅓ of the bottom edge of my screen, though it does vary in length as you change zoom levels. It doesn’t vary too much though since every halving or doubling of zoom level will halve/double the units displayed.
The difficulty is not computing the scale, but finding a way to display it without cluttering the screen too much. A little math shows that your phone is right around 4.6”, so you do have a bit more screen than some people. And when I tried it on my wife’s old phone, a Droid Ultra with a 5.0” screen, it does indeed take up a smaller portion of the screen.
FYI, the main limits on how small a computer can be these days are strictly human elements. Smartphones are about as small as most people can use for anything comfortable for typing on a QWERTY keyboard, though a T9 input could get it down to wrist-watch size… if the user has fingernails. My old Casio Databank watch was like that. Displays could get a bit smaller since objects appear larger close-up, so something like Google Glass is about the lower limit until we find a way to put a display into a contact lens. But for most purposes, the smartphone is the smallest general-purpose computer possible so long as we still interact with computers with our eyes and fingers.