This is wrong in two ways. 1) Cellphones don't just last 2 years; lots of people have older models. Sure, a bunch of people get rid of theirs after 2 years, but then they go to the secondhand market, where people like me buy them for a small fraction of their original price and keep them for another year or two before reselling them. Frequently, older phones eventually find their way to developing nations where people can't afford the latest iPhone. Your argument sounds like someone whining about people leasing a car for "only" 3 years; what do you think happens to cars after the original owner trades it in?

As for "little economic value", that's just plain ridiculous. Smartphones have enabled all kinds of things that just weren't possible or easy before: managing your bank account remotely, sending money to people (e.g. Venmo), GPS navigation, communicating without playing telephone tag, etc. And they do it with much less energy than any PC uses.