Treat the battery well (avoid wireless charging when you can, don't charge when hot) and these devices can last a long time. And even when the battery starts to die, you can get an official replacement for much less than the cost of a new phone.
If you're a typical high income tech person who upgrades their desktop, laptop, phone, tablet, and watch on a regular cycle, that's a staggering amount of money to stay on the treadmill. I'm consciously choosing to keep my devices as long as possible. I've given up smartwatches, my desktop and tablet are 8 years old, and I plan to keep my phone for at least 5 years.
Wireless charging generates a lot more sustained heat, which can, hypothetically (and in some cases has been demonstrated to) cause chemical degradation of the battery faster. Heat and high charging speeds, combined with keeping the battery at extremes (close to 0%, close to 100%) is the worst combination.
How? Apple doesn't sell spare parts. I went through two battery replacements on my iPhone SE 1G, after the original battery died. One from iFixit which was terrible. Battery SoC and performance was always wonky with that. Another from a reputable spare parts seller here, which had Apple branding on it, and it started good, but soon developed the same problem as the first.
Given Apples hostility toward repairs, it's obvious they'd rather you throw your device into the ocean and pay for a new one.
By "official replacement" I meant taking it to the store and having them do it. My wife recently got a battery replacement at the Apple Store, around $100. Paying that every 2 years is a lot cheaper (and better for the environment) than buying a new $1000 phone.
If you're a typical high income tech person who upgrades their desktop, laptop, phone, tablet, and watch on a regular cycle, that's a staggering amount of money to stay on the treadmill. I'm consciously choosing to keep my devices as long as possible. I've given up smartwatches, my desktop and tablet are 8 years old, and I plan to keep my phone for at least 5 years.