That's why they created airpods, watches, homepods and the forthcoming airtags and glasses. Those items don't get purchased standalone; they're part of the iphone experience. Analyzing iphone sales without accessory sales is missing the point.
As you said, its pretty obvious the Smartphone market is full, Apple since years looked for other ways to monetize. Thats why now Apple services have more earnings than iPhones. Apple strategy now is to keep the customer at home buying watches, headphones, tablets, Music etc... etc...
Regarding the sale of iPhones itself it would make sense to compare it per regions and against other competitors like Samsung and Xiaomi. I suspect they sale way more phones smaller and less income markets.