Will I lose my subscription, playlist or favorites after changing phones/uninstalling/reinstalling?
Of course not.
Your subscription (tags), play status, playlist, favorites or history are supposed to sync automatically once you sign in with the same account as before. However, the downloads and the app settings will not be transferred to the new device.
Please note that since Castbox offers different login methods, if you selected different entries to sign in without linking them inside the app in advance, Castbox will recognize them as different accounts.
To link your Facebook, Twitter, Google or Line accounts together to one Castbox account, please go to Personal - Settings - Linked accounts. Then you can use any of them to log in.