My car doesn’t have navigation, so I can’t answer for that, but on all models, from all world markets (according to 3 years reading this forum) the phone only plays through the speaker on the opposite side to the driver. It is designed that way.
My previous 2 Vauxhall’s, a Ford and Citroen all worked that way on Bluetooth and all cars that I’ve driven since the early 90’s with proper car phone kits have been this way. I believe it’s to do with stopping/controlling feedback through the microphone and has never been an issue.