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.
XAPO was not let the users to take or export their privatekey address and that's a scam wallet. For me to use offline wallet which make you able to get your privatekey is more than good but it's the best way. XAPO was a scam wallet. but this time so many wallets creating the export feature.