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.
Mobile wallet are easy developing by everyone to scaming use popularity bitcoin, I saw on playstore has alot of mobile wallet 'shit wallet' and use Bitcoin as key search on playstore. You have to go
https://bitcoin.org/en/choose-your-wallet and choose one there for mobile wallet