Hi,
This was a bad experience with google pixel. All of a sudden microphone is not working after 13 months of usage.
Went to Service center to address the issue and got that a complete Motherboard replacement can fix the issue. I didnt go for this as its costs me more.
I looked into several blogs on this and finally got a solution at lower cost.
'Qualcomm WCD9335' chip replacement can fix the microphone issue.
[guide|71237] this will help you to open google pixel.