Did you do a restore of your phone? The Sonos controller app possibly reinstalled, along with some previous configuration data. In that case just reset the controller and tell it to connect to an existing system when it restarts.

When you say reset do you mean delete and reinstall?

That would have the same effect, but I actually meant using Settings/App Preferences/Reset App. (Or you could go into the Android app settings for Sonos and clear the cache and data. Same difference.)