This is news? Of course you can reheat it on the skillet, you just need to keep the heat on low-medium, so you don't scorch the bottom and leave the top still cold or room-temp depending on whether or not you were sober enough to shove the leftovers in the fridge.
Anyway, the skillet isn't really the optimal way 'cause skillets are too small (only room for a slice or two). Just shove it in the oven at about 150C for maybe 10 minutes. Same effect (crispy crust, melted cheese) but you can do the whole thing at once and don't have to worry about scorching it at the same time. As a bonus, you can grab a few slices out of the oven, turn the oven off, and close the door. The remaining slices stay quite warm for about 30 minutes, give or take.