Then the p2p network is really the “server” and the phone is still just a client. I’m also not sure that a p2p network could be queried very well because something would have to be able to produce aggregated and sorted results. It isn’t like pulling one file from a swarm. It would be like a blockchain and the phone would have to download the whole dataset from the p2p network before running queries on it.
What you are talking about sounds kind of like the Nostr protocol. It is a distributed social network trying to solve the same problem that ActivityPub is but in a slightly different way. All the events are cached on multiple relays and the client applications query those relays looking for information that gets aggregated and sorted on the client however it wants.