I’ve had similar thoughts. I currently have an iPhone 6S, I’ve had it for 30 months, and don’t really have a need to change it. I remember when I started changing laptops only when they broke, and it’s a similar feeling
One interesting thing about the my phone is I managed to crack the screen on the 3 iPhones I had before, sometimes multiple times. I've put this one through hell and back and it just keeps going. I wonder if the build quality (not just features and performance) has been a factor in slowing upgrades...