Your Interest Account is custodial (unlike the funds you store in the standard Private Key Wallet, which is non-custodial). This means that it is not backed up by your wallet backup phrase. Your Interest Account is associated with your Blockchain.com identity profile. If you lose access to your Blockchain.com Wallet, all you need to do is use your Secret Private Key Recovery Phrase to recover your wallet and then get re-verified in your new wallet to recover your Interest Account funds.
Please note: the Interest Account is not a bank deposit and is not backed by any governmental deposit protection regime. Your rights in connection with the Interest Account are governed by the contractual relationship you enter into with Blockchain.com via the User Agreement. You can read the full terms here.