There's no other answer that is reasonable but the one you picked. I don't know about you, but when I'm at home talking, I sometimes use my hands as punctuation. Both my wife and I talk with enthusiasm. That word might is very strong and very important. It means he's talking on the phone while the other hand MIGHT be on the wheel. If he's in a fight with the other half, he might have one hand on the wheel and he might not.
So go with what you think.
Answer
while is the answer to the question
