I've run into this problem too. I'm using a OnePlus One. Randomly in every phone call the other person will suddenly not be able to hear me anymore. But I don't think it can be just the phone: just today, someone tried to call me back after they thought the connection was lost (I could hear then on my OnePlus One but they couldn't hear me), so I switched to answering through my laptop —*and they still couldn't hear me.
I've temporarily switched to using my carrier's phone service directly for phone calls to get around this problem, but that's annoying and I'd rather use Voice. Any help with this would be incredibly appreciated. I'm honestly dead out of ideas about what to do about this.