How long should a $999 iPhone last?

I usually spend about $1,300 on a new computer, and I usually expect it to stay in good shape for about four years — if not more. So if I’m spending over $1,000 on an iPhone, how long should I expect to use it for?
Smartphones have never had the longevity that modern computers have, often staying current for only two or so years. There are a good number of reasons why: For one, smartphones are historically cheaper, so it makes sense that companies would expect them to be replaced a b