Turn down the ISO
The Techlicious article says that high ISO will “crank up the sensitivity” of your phone’s camera so it can see details in the dark. Since fireworks are usually bright, it might not be the best option to do so. Therefore, by turning it down on your phone’s camera, take your camera out of Auto ISO and change the setting to ISO to 100 or lower.
To do so, the article says that you can find ISO settings in either the main menu or in settings in the Camera app.