Like any other bank, everyone should have the number of your own account somewhere. Phones get lost, broken, without battery, stolen… Can’t rely just on a phone to access your money.
I leave the details in the cloud, so I can check my account number from any computer or phone. Also travel with a backup Revolut card, besides my bank cards. The last thing you need when traveling is to try to get a new card shipped to you as you’re likely moving places, not having a reliable address to receive delayed shipping, etc.
But! Revolut is all about evolution, so if they make it even easier to access things without a phone and abroad, awesome.