The choleric members of the pack would be the alphas, the leaders. They would command their subordinates, and assert their dominance using force. If challenged, they would respond by getting angry, larger, in order to intimidate and to prove that THEY were the strongest, the most fit to lead.
In current society, they often tend towards leadership roles, such as managers, politicians, captains, team leaders, and so on, though not necessarily.
The phlegmatic members of a pack might have been the obedient followers who’d get much of the actual work done at the command of their superiors. They may not stand out, but without them, nothing would work.
They are the cooks, the cleaners, the quiet office employee.
The sanguine members of the pack might have played a supportive, encouraging, social role. They would have been the glue that kept the group together.
In modern society, you might see them as entertainers, singers, dancers, or perhaps simply as the energetic people at parties.
The melancholic members of a pack may have been the analysts, the information gatherers. They scouted for potential danger, or for food, and reported back to the pack leader. The more accurate their findings were, the better; this led to a trend towards perfectionism, as the ‘analysts’ closer to perfection survived better than those that made sloppy mistakes.
In current society, they often tend towards analytical roles such as scientists, analysts, programmers, logicians, and so on.