Phone cameras just depend on the phone. I've gotten some really good pics...well *I* thought they were really good ones at least .... with my iphone. It's the 4S with the nicish lens.
It also helps if your betta is a showoff. I have one camera hound, two that don't care, and one shy one.
I also have a nice digital SLR, and while I've gotten some really crystal clear shots by being patient and going to manual focus, they are more of a pain to deal with by simple virtue of it not being an internet aware device
I agree on the natural light though, I liked the ones I took with some good filtered afternoon sunlight the best.