I had a look at Fairphone. You have to accept some compromises compared to most on the market. I tend to go for a budget phone and hope it will last a few years. I don't think the technology is changing as fast these days, so it should be viable to keep them longer, but the manufacturers tend to stop issuing updates and you need security issues to be dealt with. We need legislation to compel them to offer longer support. I would be prepared to pay something for it.