Microphone not working unless using speaker

Hi @stephroux

Is the phone in a protective case?

If it is remove it from the case and check if you can be heard OK when on a call. It may be accidentally blocking the voice inlet hole to the main microphone, on the bottom edge of the phone. The speakerphone uses a different microphone found at the top of the phone.

If not in a case or even if it was and it still doesn't work OK after removing it from the case, then the voice inlet hole on the bottom edge of the phone may be blocked with lint etc.

Here's an image taken from the ifixit Google Pixel 3 充電アセンブリの交換 guide to show where it is located in the phone

(click on image)

Use a vacuum cleaner and see if this clears any obstruction from the voice inlet and that the phone now works OK. Do not use a metal pin or probe to try and clear the hole as you may damage some components that lie directly behind it e.g. the microphone.

If still no good the phone will have to be opened and further tested as to what is wrong. It may be a faulty microphone for example.