A backup phrase is a combination of twelve random words that grant access to your funds. It comes to the rescue in case you want to transfer your assets to another wallet. For instance, if you've lost your device and want to restore access to your wallet, the backup phrase will do you a favor. Or, if you forgot your passcode, you need your backup phrase to regain access to your crypto.
If you haven't saved your backup phrase at the beginning, don't worry. Just go to the Setting tab at the bottom, scroll down to the Security section, tap View backup phrase (please, make sure you are doing it in private!). Make the final tap to copy your backup phrase, and please save it in a secure place, preferably offline.