what does it mean by built in wallet? it could mean that it's a wallet app pre-installed but you can always install it from playstore.
The phone comes with a separate hardware chip inside. The Samsung Blockchain Keystore is part of the OS, not a separate app you can download or delete. This controls the hardware chip. The Samsung Blockchain Wallet app I think might have come pre-installed, but you can download it from the Samsung Galaxy Store (it is not on the Google Play Store). You can download the APK from other sites though, but I would only get it from Samsung.
Samsung's Blockchain SDK hints at being able to connect to a Ledger with an OTG cable, but I don't know if that has been developed yet.