Mm, hm, uh huh, yeah, ok.

By default, a mom listens to many phone conversations, because the phone is in the kitchen or within earshot.  Of course, we have to pretend not to hear them because we aren't part of them.  It's kind of like cubicle life. There is a proper protocol. Don't comment, don't interrupt, never mention what you heard. 
My daughters all have babysat and have developed great relationships with their families. One family, in particular, has used all of them over time, so we are like their family. I always know when my one daughter is talking to the mom because she says, "Mm, hm, uh,huh, yeah, ok. Mm hm, uh huh, yeah, ok." Over and over and over. Finally, when I couldn't take it anymore,  I have to ask, "What is she saying?' Mt daughter tells me, it doesn't matter. It's the fastest way she can get through the conversation and get off the phone without being rude.  I thought about that for a long time. She was only 14 and yet she had discerned a very important fact. Non-committal verbalizations get you all the information you need, in the quickest time with no input on your part. So I decided to turn it around and try it on all of them.
When the moment happens, and they open up, the less you say and do, gets you the largest yield.  Here are a few more - oh? ooooo, wow, gee, whew, yikes, aw, ew. I mean, really, it's kind of pathetic. They aren't even real word or more than one syllable.
But they work. So does, no emotion, no reaction, no facial expressions. Neutral, nothing, silence.
It gets you all you could possibly ever want.
I promise.
Try it. When they have something to tell you, you (need to) have nothing to say.