Natalie Coughlin gave the Americans an early lead in the backstroke -- nearly 1 seconds ahead of Sophie Edington -- but the Australians surged to the lead with breaststroke world record holder Leisel Jones.
Jess Schipper (butterfly) and Libby Lenton (free) finished off the dominating win.
"We have such an awesome team this year," Schipper said. "I'm just glad to be part of it."
The US team grabbed the silver in 3:59.92. Germany took the bronze, while the Russians were disqualified.
Australia's Danni Miatke won the 50m butterfly, a non-Olympic event. The next two spots went to a pair of Swedish swimmers, Anna-Karin Kammerling and Therese Alshammar.
"People ask you when you say that you're a swimmer, `Are you any good?'" Miatke said. "Now I'll be able to tell them, `Yes, I'm a world champion.'"
While Phelps has won four golds medals and, now, a silver at the world championships, he's not happy with his performance. He failed to qualify for the final of the 400m freestyle and was a disappointing seventh in the 100m free.
Two of his four golds have come on relay teams, and Grant Hackett is likely to win the most individual medals on the men's side. The Australian star already has two golds and a silver, and he's an overwhelming favorite in Sunday's 1,500m free.
"Everything that has happened this week is a wake-up call," Phelps said. "It's all going to be used for motivation."
Crocker is motivated to become the first swimmer to break the 50-second barrier in the 100m fly.
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