We demonstrated the temperature-dependent 2D phase behavior of DPPC monolayers simulated at various areas per lipid, spanning high and low lateral compressions. The monolayers exhibited LC and LE phases at high and low compressions, respectively, along with coexistence of the two phases at intermediate compressions. The phases were characterized using parameters representing local monolayer thickness and lipid tail order. At lower temperatures, the LE phase within the coexistence regime tended to form a gas phase, characterized by low-density regions containing lipids oriented parallel to the interface. This low-density regime suggests the potential coexistence of LE, LC, and gas phases at the triple point temperature (~290 K). As the temperature increases, the LE and LC domains become smaller and smaller, and mix upon reaching the critical point.