So you know how it's possible to transfer a whole bunch of accounts through google auth from one device to another via a QR code? Turns out that works much less well if you've managed to drop your phone such that the screen shatters.
I finally got enough of the codes transferred by taking pictures of the codes on the smashed screen and tweaking them in gimp until it was good enough to scan with the new phone.
(I am now backing my 2FA details up to the cloud)
I guess I could have used the old phone, even with a smashed screen, to generate codes to log in and just delete and then re-add 2fa. Oh well.