Phoenix was considered on the same level as Heavenly Beast on their own. A mythical creature with power many desired. Not just the Sacred Realm, but also the people from the God Realm.
The phoenix fire didn't just contain destruction, but also contained healing ability. That was what the current patriarch tried to achieve, the perfect and pure phoenix fire. That was why they killed the phoenix and used its remnant to generate phoenix inner energy to help with their cultivation.
Even so, they failed to achieve the desired result. Hundreds of years passed, and they could not reach their goal after slaughtering the phoenix. It was not that they didn't make progress, but it was far from the desired result they wanted.
Feng Zhan was one of the few who opposed the idea of slaughtering the phoenix. But he didn't have the authority or the power to stop his brother and others from his family. However, he was the first one to achieve their goal.
