Story
You headed to the Aullaeu underground altar with the key you obtained from Aulamus. Go inside the altar and track down Reda's whereabouts.
After completion (spoilers)
"It's too risky to leave the Core to Reda now." The underground altar was filled with Aullaeu corrupted by dark magic experiments, and wraiths summoned by that same magic. Deep within the altar, you found a photo of Reda's daughter, Teina. Reda had used Scarlotus to revive her daughter. Considering Reda's actions so far, it is unlikely she has stayed true to the duty entrusted to her. For Phernos, duty matters above all else. He declared he would stop at nothing to take the Core back from Reda.