Chosen Solution
I have a problem that I cannot understand why. Firstly, i noticed that Siri did not hear me and also my friend did not hear me when we video talking on WhatsApp. I researched this situation and found. I need to replace the flex part consisting front cam, front mic, proximity sensor and light sensor. I ordered the new one and picked it up then I replaced it. I tested front mic on WhatsApp video talking and selfie video so it worked but proximity and light sensors did not work despite front cam and mic worked. So i sent the part back and I ordered a new one that I was sure was original. I replaced it. Now front cam and sensors are working but front mic still has static noise when I recording a video with front cam.
The supplier that is providing you the front camera flexes is probably no good. I would move onto another seller if you know that the front camera assembly is being installed properly. I recommend going over the guide for replacing front camera on iFixit just in case: iPhone 6 Front-Facing Camera and Sensor Cable Replacement
