Pioneer car radio avic 5100 next mic doesn't work

There may be settings in the menu to select internal or external mic. Check your menus to see if you have the right option selected. Try a different wired mic to see if that works. Or check the mic's wiring to make sure it didn't get cut during installation - that's more common than you think. If you're trying to use the head unit's internal (built-in) mic, check the menu settings to see if there is an option to use the phone's mic instead of the head unit's mic. That might be selected by mistake.