Everything you keep in Whimbrel, your notes and any recordings, is stored on your phone and nowhere else. Whimbrel's data is not included in Android's backup to your Google account, so a new phone does not bring it with it.
Uninstalling Whimbrel deletes everything it stores. Before you change phones or uninstall, export the notes you want to keep: they come out as plain text, which you can save or share wherever you like.