This is for smaller phones, like the iPhone 1-4, the iPhone 5 might be too long. If you have a very bulky phone, don't buy it. It works perfect for what I have. I have a Samsung Eternity, and it has approx 0.7 centimeters of extra space in length.
Spill-proof. 100% polyester. Lightly padded case, it's not an otter box though, do don't go throwing it off a two-story building.
I bought a Dakine backpack too, and it fits perfectly on the shoulder straps. It should fit any brand of backpack (The North Face, Volcom, etc). It doesn't really slide up and down the straps, unless I deliberately tug on it, which is good, or unless I hit major bumps on my bike.