Every year, I pay the whole cost upfront for the biggest, fanciest iPhone unlocked directly from Apple. This year, I will be selling my iPhone 11 Pro Max (256 GB) on eBay and buying the same size 12 Pro Max. I should get about $900-$950 for it as it is in mint condition. Accounting for eBay fees, PayPal fees, and the taxes I'll pay on the new 256 GB Pro Max, it will essentially cost less than $500 for me to upgrade.
Older iPhones obviously lose value each time a newer model is released, so I am paying only a tiny bit more than if I upgraded every 2 years or every 3 years and did the same thing. I would start saving serious money only if I kept my current phone for at least 4 years, and as a tech enthusiast I just can't bring myself to do that -- especially considering that this is a device I use for multiple hours every day.
In other words, upgrading your iPhone every year is actually not stupid or particularly expensive assuming you pay upfront, keep it in good condition, and sell the old one on eBay. Using this method, I am paying only a fraction of what those on Apple's yearly upgrade program pay. I understand that not everyone is in the financial position to do this, but if you are and are a tech enthusiast like me, I think this is the best way to do it.