Microphones on iPhones are typically placed at the bottom near the charging port, at the front close to the speaker, and on the back near the camera. The easiest way to verify if they are functioning properly is to launch the Voice Memos application, speak, and then listen to the recording to assess the sound quality. Besides that, making a phone call or recording a video can be used for testing various microphones. First of all, check that there is no dirt or any case obstruction covering the mics. If the sound remains muffled, you may use a soft cloth to clean them and reboot your gadget; however, if the problem is still not fixed, getting a professional repair might be necessary.