Michael Phelps Got Katie Ledecky's Autograph!

How cool is this ... Michael Phelps and Katie Ledecky recreating that famous 2006 autograph photo -- IN REVERSE!

When they took the original pic back in 2006, Ledecky was just 9 years old -- and Phelps was her aquatic hero ... having just racked up 8 medals at the '04 Olympic games.

Now, it's Ledecky who's killin' it in the pool -- she just scored herself 5 medals (4 gold!) and blew her competition out of the water.

So, it was only fitting for Phelps to turn the tables on Ledecky and ask for HER autograph.