Agreed, I have an extra phone for gmail authenticator backup, also make sure to secure a pin code, you can use a paper or something and store in properly.
Back up is very advisable to save files in case of any emergency cases like you lost your phobe or someone stole it from you. You can have other phone or you can also save file to your laptop, hard drive or even flash drive. I personally back up files on my flash drive with OTG so it easily back up my files on my phone.