Is there a way to add hardware into a phone that is separate from the phone itself but can still interact with it from the inside to sign transactions and truly keep your bitcoins in your phone?
The BitBoxApp is available on Android so you can manage your crypto on the go. Simply download the Android app and connect your BitBox02 using the convenience of USB-C.
I don't know if you were thinking of something like that, but maybe it looks like it.
In this case you have indeed two devices : smartphone and cold wallet, but if you don't have a pc, it's still very practical and above all very secure.
https://shiftcrypto.ch/app/