I'm no expert, but I think this is by design--not only do most people not want to have a conversation while simultaneously listening to music, but music in the background would make the audio quality of the call worse.
I'm not sure if there's a way to override this setting, but all my friends' and family's cars (of all makes and models) also cut off audio (radio, Sat, Podcasts, Audible, etc) if you make or receive a phone call.
Do you talk while driving that often that it's an issue? My mom can't drive anywhere without calling someone on the phone--it's like a smoker needing a cigarette while drinking, I swear. Personally, I don't like talking on the phone at all, but especially not while I'm driving--but we're all different.
2018 Touring L Plus | Copper Pearl | S Pkg
Advanced Safety Tec / Hands-Free Doors / Towing / Keysense