Issue when using smartphone GPS (2014 Mazda3)

Hi
We have an Australian 2014 Mazda 3 SP25.
We don't really want to pay over $400au to update the car's GPS.
Our smart phones have a great GPS system that is always up-to-date, and can even warn and re-direct you around accidents, traffic jams, etc.
However, when using our phones as our GPS in the Mazda, the audio in the phone has been muted.
Is there a way of preventing this from happening?

BTW, both phones will Blu-Tooth connect to the car, and there is not problem in using the phones through the car's audio system.
 
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