Why host anything on a phone

The honest answer is that the hardware is already paid for.

A phone that has been replaced is a complete computer: a fast ARM chip, several gigabytes of memory, flash storage, a battery, and a network interface. It is sitting in a drawer. The only thing standing between it and a useful second life is software willing to treat it as a server.

That is the whole idea. Not a stunt, and not a benchmark contest. Just a small machine doing small work reliably, for the cost of the electricity it takes to keep the battery topped up.