P2V's don't have a mic, indeed.
Those of us with non-Vision, GoPro models do indeed get sound with our recordings, but there's nothing other than the buzz of the rotors. Indeed sometimes this sound can be used to troubleshoot issues.
Any time you see a video taken from a Phantom where you can hear anything other than the rotor buzz, the author of the video has done some artful editing. For example some people will have a mic on the ground recording ambient audio, then mix it in to the video... sometimes they even sync it up with the video, usually not.
For example I took some car videos recently and now that I have 2 gopros (3+ and 4) I put one gopro in the engine bay and used it's recording for sound, while the other gopro in the cabin I used the video