My phone is three years old. It is quick, the battery still gets me through a day, and nothing about using it makes me want a new one.
Early next year it stops getting new software. Security updates carry on for another year after that, which is the part that actually matters, so this is not a safety problem. It just stops moving forward.
What I notice more is the other thing. Features the hardware in my hand could plainly run turn up on the newer models and stay there. Not because the silicon can't, but because the feature is doing a job in a launch keynote. Some of that is genuine and some of it is a line on a comparison chart.
It's a Samsung, and I don't think I'll buy another. So I've been looking at what replaces it, and the honest answer is that the shortlist is short. Every option has a different thing wrong with it. One has a support window I don't like. One isn't sold here properly. One is fine and costs what a laptop costs.
In the day job I'd call this end-of-life planning. You'd map the support dates, work out what falls off a cliff and when, and put it in front of someone with a budget. Nobody does that for the thing in their pocket. We wait until it feels slow, or until it stops getting updates, and we call that timing.
The device is not worn out. The support is. Those used to be the same date and they aren't any more.