We should probably write a dedicated article about wallet files management in Monerujo and their different uses.
If you only need to access your funds again, just write down your seed safe & secret and you will be fine. On the new phone you just restore wallet from 25 word seed and it will be all there again.
If you need to recover the same wallet you had before (with your tx notes and account names), you’ll need a backup of the wallet files stored on your old phone, manually copy them to the monerujo folder in your new one, and using the CrAzYpass (wallet files restore password) to open it again.
On a Ledger wallet, the seed is stored in there, and Monerujo is just a way to interact with it. If you lose Monerujo you can still open it on another Ledger compatible wallet.