Its done on your device, not on banks side iirc, but its an optional thing you can opt into if you wish, thats not the default config when opening an account (can also be toggled on/off at will in the app, so i'm not too worried about it tbh).
No, it's not done on-device. Think about it: they know where the merchant is for card-present transactions, so how do they know how far apart the card and your phone are if they don't know where your phone is?
