Current iPhone batteries are rated 1000 cycles. That's many years if you mostly leave your phone in standby, that will be less than a year before it significant

Current iPhone batteries are rated 1000 cycles. That's many years if you mostly leave your phone in standby, that will be less than a year before it significantly degrades if you're using it daily and not just for web/SNS browsing. That's my home's experience, if you listen to The Vergecast that's the hosts' experiences as well.