I don't think the guy is suggesting phones are great general purpose servers people should host online services on.
On their own, they are small and efficient. Proper servers need 10x, 100x, or more power just to boot. Sure, AMD has some amazingly efficient Zen 4 cores now. But cores don't exist in a vacuum. Just spinning the fans on such a machine consumes more power than a phone could even dissipate.
Not saying about what and where anyone should run, all I'm claiming is that mobile phones aren't actually that efficient, they just sleep a lot and that's how they get low power draw
On their own, they are small and efficient. Proper servers need 10x, 100x, or more power just to boot. Sure, AMD has some amazingly efficient Zen 4 cores now. But cores don't exist in a vacuum. Just spinning the fans on such a machine consumes more power than a phone could even dissipate.