The old queen had always taught her children to be ruthless - one would have to be, to survive and feed. Like many others, Pharynx was trained to be a soldier-class changeling: Someone who protected the Hive from outsiders, took in prisoners, and guided troops under the leadership of their Queen. Due to his skills, it wasn’t long before he became a general of the army.
He was one of the several changelings leading the attack on Canterlot, in charge of more than just other soldier changelings.
After the reformation of Thorax, the Queen was exiled. For the first time in his life, Pharynx felt…lost. He and a few others didn’t change, still stuck in their ways from Chrysalis and giving Thorax a hard time. Some of them even questioned Thorax’s leadership skills, as he was just a Hive maintenance worker, what could he know about leading a whole Hive?
Yet they too, in time, opened themselves to their siblings and transformed.
While Pharynx remained dark and hardened. Someone had to stay on their guard, to protect and scavenge for the Hive.