I read through this thread, and I didn't see anybody else mention this possibility for the problem.
In our 2013 Sportwagen, I have no problems at all. Nobody complains, everyone can hear me, and I use it all the time. But when my wife drives, she's completely impossible to understand. We have identical phones, so I don't think the phone is the difference. But riding as the passenger with her driving a few weeks ago, I think I found the problem. The stupid microphone is in a terrible spot. It's behind her mouth while she talks. So I had her try it out while trying to look up at the ceiling, and the sound improved dramatically.
She's 5'2" tall. So she's on the short side. But she's not tiny by any means. But they positioned the microphone so far back in the car that someone her height, once she's positioned the seat to get the clutch pedal all the way to the floor, is sitting in front of it.
Are any of you other guys having issues a little on the short side?