There are 8 Sanctum Monks in the area (1 Monk, 1 Knight, 2 White Mage, 4 Rangers). Be sure to bring a tanker with some hate increase to help deal with the Rangers on the side. In the fight, the monk will always get first turn, and will always start with "Store" ability, increasing his attack from 704 to 1661 (+957 ATK). It's recommended to either dispel him, or try and burst him down as fast as possible, otherwise, the 2 White Mages will be using Curaga and Shell on the Monk. Once the Monk is down, the Rangers should be the next priority since they are the ones always attacking, or go for the White Mages if your damage is high enough to one shot them.
Sanctum Monk (Monk) Stats & Resistances
Max Level Stats
DEF Up, SPR Up, Charm Res Up, Petrify Res Up, Toad Res Up, Stop Res Up, Disable Res Up, Doom Nullified, Accuracy Up, DEF Debuff Res+100%, SPR Debuff Res+100%, Area Attack Res Up, DEF Piercing Rate.