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.
I used to use those "online wallet" when I was a beginner. Now I only use hardware wallet, It provides absolute security! Online wallet are best for storing small funds to use it for spending.