I assume she is using a hands free device like a speaker phone. You deserve her undivided time and attention.

I do have a question though: from whom are the calls originating?

Part of me says you need to take some responsibility in these situations. Personally I wouldn't accept any kind of conversation over a speaker phone at all and certainly not while someone is driving. I simply tell the person to call me when they have proper time to devote to a conversation. Insist upon it. There is nothing wrong with doing so. To continue conversing though is giving the other the message you find such behavior acceptable. Put your foot down.