The X is fast enough with great camera and still good battery life although I can tell the battery is starting to loose noticeable capacity, still fine for daily use.
Will probably upgrade to a 12 which will be a three year change. Apple has kept me happy with ongoing software updates, I can hand the X down and it will continue to be supported for a couple more years and be useful.
I can see the trend continuing though where I might go 4 or 5 years or more between phones as the tech gains become smaller and battery life extends. They become more like cars (which I typically keep 10 years).