Apple's iPhone 15 Pro Max is undoubtedly the best iPhone the company has ever made for a few reasons, and not just because it has the fast A17 Pro chip or the biggest and best display yet offered in an Apple-branded phone. Another reason beyond those is the addition of Apple's first tetraprism camera lens, a lens that allows Apple to fold light and create a new telephoto lens that can manage a 5x optical zoom. That beats out the 3x zoom of previous models, and the telephoto lens still used on the iPhone 15 Pro. But now it seems increasingly likely that Apple will bring that same lens to the iPhone 16 Pro.
It was said that the tetraprism lens didn't get an iPhone 15 Pro release due to the smaller size of the phone impacting Apple's ability to physically fit it inside. However, it now appears that Apple has been able to fix that problem and the 5x zoom lens is now coming to the iPhone 16 Pro.

That's according to a report by MacRumors which matches similar reports by The Elec and analyst Ming-Chi Kuo, claiming that both the iPhone 16 Pro and IPhone 16 Pro Max models will sport improved zoom offerings when they go on sale in or around September 2024.
As for how the new lens is expected to fit in Apple's next Pro iPhone, it's thought that Apple is going to extend the size of the display from 6.1 inches to 6.3 inches, making the overall size of the phone just large enough to accommodate the new lens. The iPhone 16 Pro Max is also expected to see its display size increase from 6.7 inches to 6.9 inches, too.
It's worth remembering that this information might not match up with what Apple ships next year, with MacRumors noting that it relates to pre-production hardware and as such might not match the finished product.