Welcome to Android Central! Check the primary mic opening at the bottom fo the phone, and make sure it isn't blocked (e.g., by the phone's case, or by lint clogging it up). The voice recorder typically uses the secondary mic, so that probably doesn't tell you anything about the primary mic. You could also record a video and then play it back with headphones plugged in -- if you only hear sound from one channel, then the primary mic is blocked or has failed.