When I feel that I have to upgrade because the phone slows down or that newer apps aren't available on my OS version anymore, I move over to the opposing team so as to avoid incentivizing short-lived phones too much.

So far, I only owned 2 phones in my life (didn't need one before the smartphone era), an iPhone 4S and a Google Pixel 3. For now, the Pixel 3 is doing great, battery life is not so good but holds the day.