Your Nikon D3100 would be a better option than the cell phone as you have much more control over the settings than the cell phone.
I use my Nikon D3300 and a 10-20mm wide angle lens for light painting. I set the camera on a tripod and set it to manual focus, bulb mode and use a remote trigger to activate the shutter. Depending on how dark it is outside, how bright your background is and how bright the drone lights are, you will have to experiment with your ISO and aperture settings. I always try to keep my ISO down as much as possible to reduce noise as the sensors in the Nikon D3000 series cameras are not the best at managing noise.
With that being said I like using my D3300, 10-20mm combo as it is light, portable and compact and I don't feel like I am hauling expensive camera equipment out into dimly lit areas where I am all alone.
Here are a couple of examples: Both images below were shot at ISO 100, Spirals f/8, Stars f/9. For the spirals, the drone was programmed to fly all 3 sprirals, I just stopped and started the the shutter at the beginning of each spiral (3 stacked shots). For the stars, the image is a composite of 3 stacked images as well.
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Hope this helps.
Chris