It doesn't really make sense to talk about a single product from a single supplier when talking about supply and demand. You completely leave out the competition side that drives the whole system.
A single example of gravity not working means the theory of gravity doesn't work, unless you mean that economics should not have scientific scrutiny.
Economics is in a dire state of proving theories right. It only accounts for perfectly rational actors. A famous nobel prize winner was proven wrong in the same year or so and he said his graphs didn't account for it.
In practical terms, yes. Adjusted for inflation, a modern iPhone costs roughly the same as the ones in prior generations, except now you get a lot more bang for your buck with better battery life, improved camera, etc.
iPhones aren't a monopoly (yet): they have to compete with Android phones still, plus Apple probably prioritizes increasing their marketshare and retaining customers over maximizing profit from iPhone sales. iPhones generate a lot of other profits from things like the app store, not just from the phone sales, so pricing the phones maximally would hurt those.