Occasional Voice Prompt for Phone GPS Fix?

I have one of the radios in my 2015 with the touchscreen, no navigation. It allows me to connect my phone (iPhone 6s) via bluetooth or usb port, and for the most part, works pretty well at receiving/making calls, receiving text messages. Occasionally, it decides mid-trip, that it wants to disconnect my phone from the head unit randomly - not a deal breaker - when I notice, I just go into the settings and reconnect my phone via bluetooth.

The one thing I haven't been able to figure out is, occasionally, when I use my phone for GPS either through Waze or Google Maps, its 50/50 that it will provide voice prompt for me through the speakers when I am using FM or XM radio. When looking at the head unit screen when it gives me those prompts, it looks like it is simulating my phone making a call in order to play the directions through the speakers, then once the voice prompt directions are done, the call 'ends' and either FM or XM radio returns. Has anyone figured out how to get this to happen 100% of the time that they use their phone as GPS?

I can't figure out what I am doing in order to have it work or not work in order to consistently replicate it (plug in USB first, then open maps on phone // open maps on phone, then plug in USB // plug in phone before turning the truck on // plug in phone after truck is turned on // etc etc.). I've tried a bunch of different iterations and can't seem to figure out the pattern. I really think its a good feature to play the directions over the radio since I don't have to look at my phone where to turn next if I'm driving somewhere unfamiliar - just can't get it to do it every time is driving me nuts and I'm sure it's a simple fix. Thanks!!

 

Also, am I the only one experiencing this or is anyone else having success/not having success using their phone gps over their truck speakers?

 

Mine sometimes goes through bluetooth, sometimes doesn't. The other thing is that when making a call, sometimes it connects and I hear it ringing, sometimes it doesn't let me hear it until the person has said hello. It's not consistent.