DO NOT READ IF SENSITIVE TOWARDS ANY MYTHOLOGY. People may speak of eating your favorite beings, please be prepared for such.
To start off, While I am a pescatarian, I think biblical angels would be delicious fried / grilled, specifically the ones who aren’t high enough to be abstract shapes, as I do not think I can stomach a wheel.
I think if not fleshed out in the mythology being used in the setting, it’s in the DM’s prerogative. If I were DM, I’d say the Phoenix has to actually die before it can respawn.
Slicing off a Phoenix’s wings will just result in an injured and very pissed-off Phoenix.
Moreover, I’d stipulate that whatever Phoenix parts (butchered, raw, or cooked, or even partly-digested) would disappear whenever that Phoenix respawns. And for a spicy twist: someone who digests any part of a Phoenix will have a psychic link to the Phoenix. Wisdom check after every long rest (three days after ingesting the Phoenix) to determine whether or not the person retains control of their body. Failing this wisdom check thrice in a row results in the Phoenix gaining complete control. Succeeding this wisdom check thrice in a row results in the person regaining complete control of their own body.