Not bad for a first attempt. The images are a bit pixelated. What size photos does your phone take pictures in? And/or were the images cropped from a larger image? Either might explain that particular issue.
You should certainly be able to use your scope above the minimum (15x) setting. I am guessing it has to do with eye relief. Eye relief changes as you move through the zoom range so I find I have to somewhat move the eyecup in/out from fully collapsed depending on which adapter I am using and which magnification.