Most people upgrade their phones every two years - half the voters in our poll do just that. It makes sense, most carriers lock you into a 2-year contract. And even if you buy a phone SIM-free, most phone makers are on a tick-tock upgrade cycle. You know how it goes - iPhone 6, iPhone 6s, iPhone 7... well, the iPhone 8 is 7s in all but name. Then there's the Galaxy S6 - new design but with issues, which the S7 fixed. The Galaxy S8 brought a new design and in a couple of weeks, the S9 will refine it. Then there's a nearly even split between people who change phones every year and those...
Source: https://www.gsmarena.com/weekly_poll_results_most_people_change_phones_every_two_years-news-29653.php