So basically what title says.
Im using 2FA with google authenticator for multiple accounts. What if my phone gets stolen? Can I have some kind of backup? Or maybe sync with some self hosted service?
Bonus question: what 2FA should I use instead of google?
IOS has a 2FA feature included in the key chain (passwords) settings. No need for a third party app. If you backup passwords via icloud, you are already set.
Never upload your passwords to any cloud. Always use good foss instead of proprietary software.