When you reach Aphrodite's chamber (and trust me, you'll know when you do), you'll get a short cutscene. Once you regain control of Kratos, you'll see Aphrodite lying on the bed with a "circle" prompt over her head. Approach her and press "circle" to initiate a QTE sequence.
As you proceed, Aphrodite's semi-clothed female companions will give a running commentary of your sexual prowess (or lack thereof, as the case may be). Simply complete the QTE sequence successfully to unlock this trophy.
Note that you will return to Aphrodite's chamber later in the game. She should still have the "circle" prompt over her head. If you complete the QTE sequence again, you'll get a large amount of red orbs. You can actually complete the QTE again as many times as you want, but after the second time you will only receive a single red orb, so you won't be able to use the excuse "But honey, I was just trying to max out my weapons".