Good day, just want to share my experience,
I am using 2fa as my security in my emails and exchange accounts, so one day I nearly lost my phone and that phone holds majority of my pins, 2fa, etc. so I thought I lost all, luckily I found the phone. So now I'm thinking of buying an extra phone for backup. What else do you recommend for backup?
I think they provide you with back up keys which you can use to recover your accounts if you lost your phone any time. They will also give you temporary keys 12-15 which you can store electronically or write down. These keys will always work regardless of synchronisation to open up your account and will ask you to change or upgrade the device to continue using the service of 2fa. I think they have lot of safety measures given already and you should follow them so that you wont get into trouble like this anytime.