Upgrade when something is 10x better - Eric Kim says it based on Peter Thiel's idea that you create a new category by making something 10x better.
I love this idea of combining concepts. In this case, it is the business thinking and the fire movement.
If you have a phone that works for making calls, navigation, sending texts, and photos, then keep it. A few megapixels here or there probably won't make a substantative difference in your quality of life.
Imagine a person who did not have a camera. I had a person who was driving for a ride sharing service. We got to talking about phones and he was talking about how he wanted to upgrade to a phone that I had. I still have that phone many years later. He was using the phone for work and the app, so a really cheap phone probably did make a difference.