What's that little black dot on the top of the black iPhone6 for?

The black dot is a noise-reducing microphone, and the solution is as follows:

1. After unlocking the Apple phone, click Settings, as shown in the figure below.

2. Enter the phone settings interface, and click the auxiliary function, as shown in the figure below.

3. Click the audio/video option in the accessibility list.

4. You can see the telephone noise reduction when you come in.

5. Click on the right to turn on the phone noise reduction function, as shown in the figure below.