Both microphones (Speakerphone mic and normal mic) don't work.

@badass_sunset easiest one to replace will be the main mic. It is on your sub_board (charging board). Since iFixit does not yet have a specific guide for that, use this video The charging board is readily available at many online places and not to expensive.

The sub mic is soldered to the mainboard. Use the Samsung Flowchart to test the components before replacing it.

While you work on your phone, take lots of pictures. Once you are done with it, take those pictures and create a guide for iFixit. That will help the next person that has the same problem as you do. It's easy and fun to create these guides. https://ifixit.com/Guide/new The iFixit community will appreciate this.

Repair is War on Entropy!