Jackluyt
Shaman
I think there's two options to get the phoenix fully evolved. Either focus on artifact chests (usually low value chests) and get less daily prizes and a slim chance of getting the Phoenix fully evolved based on recent Events. Or focus on daily prizes chests (usually high value chests) and get more daily prizes and a still slim chance of getting it fully evolved based on your luck on getting additional currency as those chests usually give more. So to me, I'd rather focus on daily prizes chests so at the end if it goes wrong with evolving I at least have more of them.
It'll be great to have the Phoenix fully evolved, it should not be too hard to spare one pet food per week to use it at least on Spire. We'll see how it goes.
Even if you don't get it fully evolved, there is a good chance that you will be able to craft the artifacts in a RSK (Reward Selection Kit)in future events.
This time, for example, you can use 2 new phoenix artifacts to craft the Tome of Phoenix, which contains all kinds of previous Phoenix artifacts (original, Ashen, Coldfire). You can pick which one of them you want.
Once you have made your choice, that artifact will move to your Instants section of Inventory.
There is a good chance that the current Phoenix artifact will be added next year, provided they have not found a better system of artifact management by then.