Mario Livio has a book on phi, called **The Golden Ratio: The Story of Phi, the World's Most Astonishing Number.**

It is written for the layperson, with only a little algebra. It won't satisfy people looking for the deep math, but it is great as a general popular survey of the topic. In particular, he does a nice job of separating the science from the woo (and from the unproven but plausible).