Make sure your headphone is compatible and try using different headphones to rule out compatibility issues. Clean the headphone jack to remove any lint or dust that may be obstructing the connection. Check if there is audio playing elsewhere that may be interfering with the headphone output. Verify the audio settings on your iPhone and make sure the ringer and alerts buttons are properly adjusted. Restart your iPhone to resolve any software glitches or temporary issues. Check if the audio is being channeled to another output like Airplay or Bluetooth speakers and switch it back to headphones. Disable Bluetooth and check if the headphone jack starts working. If none of the above methods work, consider seeking help from Apple support or visiting an Apple service center. If the jack is physically broken, it may need to be repaired or replaced. Double-check the volume settings and make sure they are not muted or set to a very low level.