If you have a backup, try to restore it on your new iphone. In the vast Google Authenticator didn’t restore, but I read it may now?
FWIW, this is the reason I use Authy, it works nicely with backup/restore. Beware that Authy has a cloud backup/multi device function that I personally keep off. Another option would be 1password, though I’d personally won’t mix passwords and 2fa codes in the same app.
Assuming the worst case where you can’t recover the codes, and assuming it course you never stored the offline codes, you have to go through the process of recovering 2fa.
This usually requires submitting documents that prove who you are, and waiting 1-2 weeks. So the only recommendation is to begin this process asap.
And while you re-setup 2fa make sure you either keep a backup or use an app that works when you backup+restore your phone, Im sure others will provide more options. Good luck!