I currently have a 2012 Rx 350, and am using an iPhone 7, but had the same issue when I used an iPhone 6s.
Whether I am plugged in via USB or just connected via bluetooth, the audio from my phone *sometimes* does not play thru the speakers.
The car displays shows as connected, it shows the artist/song name, time ticks by as the track plays, but the sound plays from my phone's speaker
rather than the car. To be clear: it doesn't happen all the time. Sometimes it can be fixed if I was trying to play via Bluetooth and I plug in the USB, and sometimes that doesn't help.
Sometimes it also affects calls--the call connects and shows on the display, the car cuts off the radio like it should, but the conversation is played thru my phone.

I previously had a 2008 Rx and *never* had this issue. Seeing how I've changed phones and the issue has persisted, I assume it's a problem with the car.
Any suggestions? I did buy this 2012 Rx used so for all I know, it's been an issue since it rolled off the line. Maybe there's a software update I'm lacking?

 

 

2011 and iphone 7S. I have the same problem playing music and using maps. It's inconsistent and very frustrating.