The first phones were big, then people wanted them small. Now people want them bigger. So in a few years they will be small again.
They want the screens big. They want the phones lighter and thinner than ever.
There's never been a trend to people wanting smaller screens on TVs, phones, computers or movie theatres. They accept them as a price of affordability or portability. In the old days a 25-inch TV (with a 4:3 aspect ratio) took up as much space in your living room as a comfy armchair. Now it sits easily on a counter or shelf.
Only way phones are getting smaller again is when they figure out a way for them to project a ten-inch holographic screen that feels solid out of a one-inch wide holoprojector.