Look how flat Phelps' body is in relation to his knees

Phelps just "owns" the water in just about any stroke he does. He planes when doing breaststroke rather than dragging his knees below his core. Consequently he gets a super, hydro, glide.

Some swimmers; (OK, I am one of them), have a tendency to drop their knees below their core when setting up the kick. I bet he also uses those Zoomers; I mean humongous feet of his, to push at the water for propulsion rather than just squeezing his legs together like I do.

I linked this picture from an Australian paper called, The Geelong Advertiser. The title of the article is: Aussie's will get hosed at the World Swimming Championship by the Americans. Kidding. It was more subdued and well mannered: "Aussies wary of Swim Team Invaders."