It is a problem if you are walking and the top mic is pointing away from you, on a desk where I’m talking across the top mic it is fine. The bottom mic doesn’t get used in hands free video calls etc and the top mic is very quiet compared to the bottom one. You can see the diff.
Dial *#*#66#*#* and then select Service tests > Test single > Microphone
Fairphone have recognised this, apparently it happened with update 0066 and hasn’t been fixed.