In short - never, based on the current situation.
Crypto Mining is a waste of resources - will discharge phone battery faster, will eat from the mobile data plan and may bring big bills, etc.
Blockchains who specifically state mining on phones are maybe using the phone for other purposes - access to contacts, unique ip of data connection, cpu processing of non-mining tasks, etc…
However, In our ‘decentralized web’ project we have the option of using Android phones / tablets as a bridge/ node connected on home wifi, which are forming a decentralized network -
Decentralized web — network architecture, participants and evolution