There are a few phone wallets that allow you to convert private keys to seed phrases, but most do not. This capability can be found, for instance, in the Exodus wallet. Alternatively, you can utilize a service such as MyEtherWallet to convert your private key into a seed phrase. Nonetheless, keeping your seed phrase and private key apart is highly advised When it comes to cryptocurrency security, it's always advisable to err on the side of caution because converting one to the other might be perilous.