I have the no longer produced iPhone 13 Mini (5.4" screen and 131.5 x 64.2 x 7.4 mm). It's the smallest of the later generation iPhones and I bought mine unlocked on swappa.com as they usually list a good selection of used phones. The smallest current model is the iPhone 16 (6.3" screen and 147.6 x 71.6 x 7.8 mm). Here is a link to an iPhone size comparison chart that may help:
