No the headphone jack won't affect the audio level of your phone's microphone. It sounds like when you're using your headphones that you're no longer holding your phone up by your head, so with your mouth not being next to the microphone (located at the bottom edge of your phone) it is no longer close enough to pick up your voice.
When you're using your headphones try keeping your phone close to your mouth, or at least to be more specific hold the bottom of your phone (where the microphone is) close to your mouth.
06-06-2017 10:49 AM