If you buy and hold cryptocurrency, at no time will it produce "dividends" in fiat currency, or physical objects like cell phones.
So if you make money by selling some cryptocoin, that is _entirely_ because someone else purchased it at a greater price than you did.
Their expectation is that someone else will later buy it at a greater price from them, and that person will be buying it on the hope that someone will pay yet more again.
No actual cashflows appear anywhere in this process.
What happens when there isn't a new Greater Fool?
Why it has to be physical? One could use cryptocurrencies to pay for virtual things on virtual internet, which are nevertheless thought to be meaningful.
Like, fiat currencies exist as a way of paying taxes to your government and also you can exchange them for goods and services.
Whenever you sell it, if you generated a profit on that sale, you are going to pay taxes on it (at least in the US).
That's a real value for society. Can it ever be enough to offset the added squeeze on the electricity grid (which we really don't need right now, with EVs coming on and our grid in serious need of upgrade/expansion)? Someone will have to do the math on that.