Every 4-5 years. Recently upgraded my Samsung Galaxy S6 for an S20 FE. While my old phone still worked the battery would last maybe 4 hours, so it was time to upgrade. Before that I upgraded from some lower tier pre-paid Samsung model to the S6. Maybe owned 3 other phones before that since 2004. I only use my phone for like 3 or 4 things (phone calls, Facebook messenger, an alarm clock, and occasionally reading reddit/resetera when I'm away from my computer), so while I like to have a nice phone I hardly need the newest and best. I can't understand needing a new phone every year or two unless you're really really into phone games and/or it's your primary way to access the internet. Otherwise, imo, that's a lot of money that could be spent on better things like PC parts, a nice(r) tablet, or games.