Intermittent Calls Microphone Issue which mic replace?

Hello,

When I make calls with my Iphone XS, my listener does not receive my voice each time. Most of the time when I keep silent when my listener is talking and want to answer, he cannot receive me but I hear my voice in the ear speaker. No problem with the apple voice recording app or a WhatsApp call.

When I record a video, the sound seems well in stereo.

I Already tried a restore without sucess

An apple official seller did a diagnostic and told me that the right microphone is dead and that I need to change the phone 500€ Blah blah blah.

My question is the following:

What is the part I need to change:

1. The loud speaker that may include a microphone.
2. https://fr.ifixit.com/Boutique/iPhone/iP...
3. OR
4. The Flex câble including a mic.
5. https://fr.ifixit.com/Boutique/iPhone/iP...

Thank you experts for your answers.