Apple is planning on launching the iPhone 12 this fall which is rumored to be coming in 3 different sizes: 5.4", 6.1" and 6.7".
The middle size (6.1") matches up with the currently shipping iPhone 11, but the other two sizes will be entirely new.
Over the weekend, there was some excitement about how well the new 5.4" iPhone 12 compares to the original iPhone SE.
Those who have been hoping for a smaller iPhone see the 5.4" model as possible successor to the original iPhone SE in terms of one handed use.
Note: the iPhone 11 Pro is essentially equivalent to the iPhone X in size, and the iPhone XR is the same size as the iPhone 11 and 6.1" iPhone 12.