[oscilloscope]

The Motorola Razr M was an even smaller form factor with a 4.3" display. And all the iPhones from 3g to SE were outstanding in this now-extinct category, especially the 5s.

The 5s has the venerable status of being not only small, but one of the oldest currently-supported smartphones. At over 5 years old, it can still run respectably with iOS 12.