Additionally, adjust your ISO to the highest number (mimics the film used for very low light and low speed images)
And set your shutter speed to the longest time possible (on my phone it’s 10 seconds).
Leave your focus settings on Auto, and if your phone camera has a timer option, turn that on (five seconds is generally enough).
Plan your shot first, then find a place to set your phone down so you can get the image you want. The less light pollution, the better; you’ll pick up FAR more stars in your picture.
Once you know what you want to shoot, tap your screen to “focus” it, then hit the button to take the picture, set your phone down, and back away from the “tripod”. Don’t touch your phone for a good 15 seconds, just to be sure.
You will not be disappointed in the results, let me assure you.