Lightning Phoenix — ruling 1

Lightning Phoenix's last ability triggers only if it's in your graveyard as your end step begins and only if an opponent was dealt 3 or more damage before your end step begins.

Lightning Phoenix — ruling 2

Lightning Phoenix's last ability looks at how much damage was dealt to opponents in the turn, even if it wasn't in your graveyard when the damage was dealt. It doesn't care if opponents gained life, even if they gained more than they were dealt damage.

Lightning Phoenix — ruling 3

If an opponent is dealt 3 or more damage and loses the game, Lightning Phoenix's ability triggers as your end step begins.

Lightning Phoenix : règles, fonctionnement et interactions (MTG)

Lightning Phoenix is one of those cards players keep asking about. Here is, in plain words, what its official text says, the rulings published by Wizards of the Coast, and the combos players actually run.

Official card text

Flying, haste This creature can't block. At the beginning of your end step, if an opponent was dealt 3 or more damage this turn, you may pay . If you do, return this card from your graveyard to the battlefield.

How it works : Lightning Phoenix

Original English text — Wizards of the Coast / Scryfall

#1June 23, 2020· Wizards of the Coast
Lightning Phoenix's last ability triggers only if it's in your graveyard as your end step begins and only if an opponent was dealt 3 or more damage before your end step begins.
No other card is named in this ruling.
#2June 23, 2020· Wizards of the Coast
Lightning Phoenix's last ability looks at how much damage was dealt to opponents in the turn, even if it wasn't in your graveyard when the damage was dealt. It doesn't care if opponents gained life, even if they gained more than they were dealt damage.
No other card is named in this ruling.
#3June 23, 2020· Wizards of the Coast
If an opponent is dealt 3 or more damage and loses the game, Lightning Phoenix's ability triggers as your end step begins.
No other card is named in this ruling.