It used to be simple. One iPhone, just pick the storage size you want. Then it spiraled into colors and endless variations, and feature differentiation.
A simple "one size fits all" approach could be worse. Many customers are quite content with a more basic regular phone while others may prefer a different size and/or different color and/or want all the bells and whistles. Offering only one phone which means customers may have to pay more for things they don’t want/need is not the answer.