 The Phoenix is a various beast in Hogwarts Legacy, mainly because there's only one of them. Now to get the Phoenix Legendary Bird you need to progress Deke's Quest. This means progressing past the elf, the napsack and the loom, progressing past the foul of the dead and on to Phoenix Rising. These quests can sometimes be locked and tied to the main quest story line as well as your level. So if you finish one of Deke's quests and you're waiting on another to appear, either level up further or progress the main story quest line. You will eventually come to the Phoenix Rising quest, at the end of this quest you're able to capture the Legendary Phoenix and you are able then to release him into your Vavarium, where Deke will open up your fourth Vavarium for you. Guys check out my channel for more Hogwarts Legacy.