I try to keep them about 3-4 years, I'll do a battery replacement myself if needed as thats usually the first thing to really cause problems. Battery is maybe $30 and an hour of my time. This last phone I got was a moto x4 for $150, so if it lasts me 4 years with a battery swap, TCO ~$180 for 4 years, or 60/yr. To get that out of an iphone I'd have to have it for 10 years or more.