Which part do I need to change?

Hello guys. Last week i bought an iPhone from craigslist for pretty good price. However, it has one flaw. It looks like front microphone, speaker and light sensor are not working very well.

In videos recorded via back camera sound is ok, voice memo works great, i can call without problems, even videocall on messenger works great but when i try to use Siri or record video with front facing camera, the sound is just buzzing and weir noises. When i speak directly to the grille above display it is a little better but it still sounds like whispering in a blizzard …

Another problem is the top speaker, which is a lot quieter than the lower one. Also the sound quality is worse. And light sensor is also not working (which is strange because proximity sensor works just great).

I changed battery and lightning connector on this phone, so i tried to clean up the speaker but it still does not work. Everything is connected firmly and nothing seems to be damaged. So my question is which part do i need to change?