There was a huge upgrade cycle during covid because people had ample savings and nothing else to spend money on. That pulled forward a lot of sales. Plus, most people already have smartphones and there is diminishing return on upgrading.

It should probably normalize a bit in 2024.

I doubt the iPhone will have record sales again until a really good foldable iPhone comes out that wows everyone and it's genuinely more practical than non-foldable iPhones.