I say this with an unblemished record of staunch heterosexuality: if this works, I'm going to hunt down and kiss both you and Bruce2125. I've had this problem since day one with my 2012 Acadia Denali.
Well, you don't have to worry about me kissing you or Bruce. That setting works for incoming calls only, and I don't have problem with incoming calls. My problem is that 50% of all outgoing calls initiated on the iPhone (like pressing a Favorites contact) will switch from handsfree to the iPhone itself, thereby making me manually switch it back to the handsfree kit.