This is definitely not a case of protective film covering some sort of non-existent microphone.
There are three mics, one right next to the ear piece, one next to the main (back) camera, and one on the bottom of the phone. Everything else you're seeing are proximity sensors.
We have 3 iPhone5's on Verizon and all of them suffer from the stuttering, robotic, drop out characteristics and also an overall lack of fidelity (all midrange with no presence in the high end or definition of lower midrange frequencies). We switched out one of these iPhone5s at the Apple store (that turned out to be a refurb) and it appears the quality improved a lot versus the originals. While not perfect, there is a noticeable difference especially in fidelity.
My guess is that overall on this thread, the issues are a combination of things; lack of HD-voice technology on Verizon's (and AT&T's, Sprint's) network, noise cancellation issues (hardware and/or software) and compression algorhithms (Apple's software). Whatever it is, there is no excuse for Apple/Verizon not to acknowledge and address these serious issues. Call quality on the original iPhones5s that we still have are completely unacceptable and borderline acceptable on the replacement iPhone 5 refurb we got.
Apple, are you listening? Hello???