On my Android phone I turn off the Bluetooth on the phone, and the call will transfer back to the phone.
Actually I frequently have to do this when taking calls at home, because my wife will unlock and get into her Tesla in the garage, which being right under our master bedroom is close enough for the phone to connect to her car handsfree. But it ook me several months to figure out why the middle of calls were sometimes going silent, but not hanging up ....