Cover the secondary microphones wherever they are in that phone (next to the earpiece?) if that phone has noise reduction feature.
Check my other posts about iphone 5 considering your voice as noise when the phone is not STUCK to your ear, because your voice is received through BOTH microphones (yes, Apple dictated that if you want to move the phone away your ear just 2 inches (lots of times), you should push the "speaker" button to prevent the noise reduction muting your own voice, rather than just manually activating it the few times you actually want to speak from a noisy place)
Part of the problem can be fixed: if the phone is against your ear as designed by Apple
I.e. not for reading the screen while talking for even one second, sorry.
Updated tests here: https://discussions.apple.com/thread/5136434