Can you explain this? How is the phone the server? It would be nice if you could use NOSTR for private groups of friends or acquaintances without exposing your posts to strangers, but nowadays it seems very complicated to make a relay in nostr 

 In the future, sure. People in your WIFI could connect to your phone and manage their group inside the house. But more importantly, it's important to offer a way to backup your server in your phone to avoid losing your data in today's relays.