The heavier the particle, the more energy it takes to create it within a particle accelerator, and the more quickly it decays into lighter particles. This also makes it more difficult to study such a particle's properties. It's just not around long enough to get a good look, so to speak.
Enter the QGP, which serves to slow down charm quarks as they pass through it; in fact, the ALICE scientists reported that the quarks actually seem to be dragged along by the plasma's current. (Yes, the QGP has a flow.)
And sometimes, they found, those charm and anti-charm quarks recombine to form something called "charmonium." This notion dates back to the 1980s, when such an end product was proposed as a direct signature, or indicator, that a QGP had formed. It was first confirmed in 2000 at CERN's Super Proton Synchrotron.
Neither ALICE nor PHENIX has ever been about anything so simple as hitting the hottest manmade temperatures. It's just a nice feather in the cap. So don't expect PHENIX to rise from the ashes to topple ALICE's record in turn - its scientists are much too busy uncovering evidence that the QGP may morph from a frictionless liquid to a hadron gas, a more "normal" state of matter. It's a high-energy phase transition, analogous to how water can change into ice or steam, in response to certain temperature and pressure conditions.