Not all mobile wallets have backup ,just because they are available for your smartphone doesnt mean they are reliable
Do not use mobile wallets with just username and passwords ,they are called online wallets ,they have no backup phrase or private keys.
For example I lost my bitcoin to xapo wallet since 2018 and they denied me of my coins after sending them mails.
If you use imToken, they have both of these features, after logging in with username and password. They will suggest you save the phrase to avoid losing your wallet. I suggest you switch to using it