Flamewake Phoenix’s ferocious ability triggers only if Flamewake Phoenix is in your graveyard and you control a creature with power 4 or greater at the beginning of combat on your turn. Additionally, the ability will check to see if you control a creature with power 4 or greater again as it resolves. If you don’t, the ability will have no effect.

You still choose which player or planeswalker Flamewake Phoenix attacks.

If, during your declare attackers step, Flamewake Phoenix is tapped or is affected by a spell or ability that says it can’t attack, then it doesn’t attack. If there’s a cost associated with having Flamewake Phoenix attack, you’re not forced to pay that cost, so it doesn’t have to attack in that case either.

If Flamewake Phoenix enters the battlefield before the combat phase, it will attack that turn if able. If it enters the battlefield after combat, it won’t attack that turn and will usually be available to block on the following turn.