I feel rather qualified to answer this question…
The iPhone accounts for over half of Apple’s overall revenue.
The problem is that sales are falling. Slowly — but they’re decreasing, nonetheless.
This shouldn’t come as a surprise. Apple has been marketing and selling the iPhone since 2007, and it has been an astronomical success. Unfortunately, there are only a finite number of human beings on the planet, and a lot of them have already bought smartphones.
If you live outside of the tech bubble, of which I’ve been a part for most of my adult life, smartphones are just that — smartphones. It takes either a broken screen, a failing battery, or an unmissable carrier deal to make most normal people change their device. And when they do, they’ll probably go for the latest version of what they already have. This makes life for smartphone manufacturers like Apple incredibly difficult. How do you reinvent a market which doesn’t need reinventing in the eyes of its customers?
At the moment, it seems the answer is to either make smartphones thinner or foldable (or both). And the jury is still out as to whether either of those approaches will lead to iPhone-level success.