In hindsight, I realised that I was coming from an Android phone a few generations back (Pixel 2) which I considered to be a reasonable size. Pixels have gotten about 10 mm longer over time. However now we have wall to wall screens, it's quite a difference. The iPhone Pro is the same form factor as a Pixel 2, for example, but is all screen. 6" seems doable for Android, but that's a lower bound.
I think what we all want is a Pixel 2 without the bezel. There are lots of phones with smaller OLED displays, but none without the bezel.