Inno has stated that the Phoenix Artifacts "will be available very rarely outside of this event". Which basically means, we might be extremely lucky to see 1 or 2 pop up as say the stage 3 prize of a Fellowship Adventure for example.
Artifacts will not be available to craft, but again, Inno might slip an Artifact into the treasure chest for collecting the 100 Vision Vapors? (and of course, if they ever do, you can expect it to be horriawful odds of maybe 5-15%!
)
And yes, the event is designed that, outside of spending a mountain of $$$, you will only be able to get 1 Phoenix to Lv6-7 or so in this year's event.
Now if you concentrate purely on going for the most efficient feathers/essence chests, AND, can collect 18-20 of the eggs around your city every single day, AND, finish the entire quest line...
You *might* be able to squeak out a 7th artifact, meaning you'd only need to spend diamonds for another 2 to get 1 fully leveled lv.10 phoenix.