Sounds like a skill issue

I should have given you a serious answer. I didn't give you a serious answer at first because I guess I don't actually take phone based mining very seriously, but you did need the actual info you were asking about. Answer: You can get free electricity for a phone at most libraries but they might not react the same way to you bringing your 6 node cluster to plug in. When you have to pay for the electricity, the newest phones always have newer CPU transistor manufacturing than your cluster for better power efficiency. So if anyone can make a profit on the cost of electricity to mine cryptocurrency, it might be a phone. But like I said, it's all kinda silly to me since phones aren't really secure or private enough to be as good for this as dedicated mining rigs can be.

Nothing useless about securing the network and getting paid for doing so. Running any device via xmrig just adds to the global hashes Decentralized, localised, cheap, accessible, private, anonymous, peer to peer, What more do you need?