Damien felt extremely thankful for the relationship of absolute trust shared by the Phoenix Clan Matriarchs and their daughters. If it wasn't for this, it would've taken far too long for him to gain their trust.
But Feng Qing'er and Lunaria were generally smart people. With Damien's explanation, along with his pulling them into the Sanctuary, they were able to understand the severity of the situation easily.
After all, something like the Sanctuary was a card that Damien would never show to people he didn't have absolute trust in, and no matter how much Feng Qing'er didn't want to admit it, she knew she wasn't included in that group.
With Feng Qing'er by his side, Damien was able to gain the Fire Phoenix Clan's cooperation within no time just like how he had done with the Ice Phoenix Clan. Messengers and guides were dispatched in an instant to gather all their forces into the palace.