A phenotype would be the actual characteristic. The genotype would be the letter representation. For example, say you have one gene for blue eyes and one gene for brown eyes. That would mean you were heterozygous. The genotype would be Bb. The phenotype in this example would be brown eyes since that is the dominant trait. I hope that helps. :)
Definitely true for kidney stones. Not sure about gallstones as they are formed I believe from buildup of fatty waste from hypercholesteremia. Less fluid volume in the body could cause these substances to aggregate in the liver/gall bladder instead of being broken down/filtered and flushed out in the bloodstream and GI tract, so I would say true
Though all choices protect your organs the most important would be your bones.