The 21-year-old American slashed almost a second off his own world record to win the 200 metres individual medley final after setting the best ever time for 200 freestyle and 200 butterfly the two previous days.
The U.S. posted two more world records in the Susie O'Neill pool to continue their domination of the championships in the lead-up to next year's Beijing Olympics.
Natalie Coughlin, Dana Vollmer, Lacey Nymeyer and Katie Hoff combined to smash Germany's 4x200 freestyle world record and Leila Vaziri equalled her 24-hour old time of 28.16 to win the 50 backstroke gold medal.
Italy and Canada both collected their first golds of the championships when Filippo Magnini and Brent Hayden dead-heated in the men's 100 freestyle final.
The pair touched the wall in the identical time of 48.43 seconds to share the honour of being the fastest men in water and producing the first dead-heat in any event at a world swimming championship.
Jessicah Schipper provided Australia's fifth gold medal of the championships with an all-the way win in the women's 200 butterfly final ahead of American Kimberley Vandenberg and Poland's Olympic champion Otylia Jedrzejczak.
Phelps is chasing an unprecedented eight world titles in Melbourne and few would bet against him after his amazing performances over the first five days of competition.
NEW LEVEL
Phelps has been a serial record breaker since he broke his first world mark as a 15-year-old in 2001 -- the youngest man to achieve the feat -- but his performances in Melbourne have elevated him to a new level.
"To be (mentioned) with the names of guys like Tiger Woods, Roger Federer, some of those guys are just incredible," he told reporters.
"To be able to be included in that is a pretty big accomplishment and something to be proud of."
Phelps's winning time of 1:54.98 slashed 0.86 off the previous record of 1:55.84 which he set at last year's Pan Pacific championships in Victoria, Canada.
His American team mate Ryan Lochte finished second in 1:56.19 after pushing Phelps most of the way and Hungary's Laszlo Cseh was third in 1:56.92.
Magnini, 25, joined American Matt Biondi and Russian Alexander Popov as the only men to win the 100 freestyle event at successive world championships, while Hayden provided Canada with their first world swimming champion in 21 years after a lung-bursting finish to the final.
Australia's Eamon Sullivan grabbing the bronze medal in 48.47 with just 0.38 separating the eight finalists at the wall.
"In the last 15, I was seeing God," Hayden said.
"There is always a point where you feel like you have hit the wall and that is what I felt when I was 20 out.
"But I told myself you have come too far not to do this. So I didn't take a breath and put my head down and went as fast as I could."
Pieter van den Hoogenband of the Netherlands finished sixth to continue his run of near-misses at world championships.
Although he is the fastest swimmer in history and has won the past two Olympic titles, the 29-year-old has never won a gold medal at the world championships.
