For the first phase, stand in the very middle of the room. This is risky, but spotting the real Phantom Ganon is much easier to do from here - you can get an almost 100% success rate. Look for the shinier one and don't wait before firing.
The second phase can be optimised by standing as close to Phantom Ganon as possible so as to minimise the time wasted when the fireball is in transit. Once he is hit, do a quick jumping attack to do some damage while he is still falling, and then, once he's on the ground, quickly do repeated Power Crouch Stabs. Two stun cycles is a minimum.
The Heart Container appears near the spiky gate you entered through.
|Bosses in The Legend of Zelda: Ocarina of Time|
|Gohma | King Dodongo | Barinade | Phantom Ganon | Volvagia | Morpha | Bongo Bongo | Twinrova | Ganondorf | Ganon|