

FWIW, Android offers a one-handed mode to shrink the available screen estate so you can reach the top of the screen with your thumb. It needs to be enabled in settings once and can then be toggled by double-tapping the home button or a swiping gesture at the bottom of the screen.
In my experience (6.1" Samsung Galaxy S2x user with slightly above-average hands) this is a good compromise between occasionally wanting to do things one-handed on the shrunken screen, and still being able to hit the right keys on the on-screen keyboard most of the time on the regular-size screen.
Bing DuckDuckGo says the iPhone has a similar feature, though I haven’t touched one in years so can’t say anything about it.
That’s why I’m driving a 1994 Geo Metro.