I use two phones... work and personal.
Only one can be active (never seen a car bluetooth that allows more than one tbh)
To toggle, select the phone mode for the display, hit the setup button bottom right, click "select device" (I think its called), choose your other phone.
As for why is the Polo getting better gear? That will be because it was refreshed after the Golf Mk7... they have car net and mirror link and all sorts. But it is still a Polo ;-)