I think of phones as a 3 year replacement cycle. Though I am in year 4 with my 6s now. I get the manufacturer's original warranty plus the additional 2 years of repair or replace from my American Express card. One upside of keeping longer is that I am personally contributing less to the e-Waste problem than if I went through an Android phone per year.

So ballpark math, a $900 iPhone XR would be covered by either Apple or American Express for 36 months and cost me $25/month to maintain. I effectively run a leasing program for myself inside my small business budget.