What is the name of the boss that guards the Phazon Suit in Metroid Prime?

The boss that guards the Phazon Suit in Metroid Prime is the Omega Pirate. Samus fights this massive, heavily augmented Space Pirate in the Elite Quarters of the Phazon Mines, one of the game’s toughest battles.

The Omega Pirate is protected by armor on four limbs and uses a mixture of energy weapons, shockwaves, missiles, and supporting Beam Troopers. After its armor is damaged, it turns invisible and relocates among pools of Phazon. Samus must use the X-Ray Visor to reveal it and attack its vulnerable body before it recovers.

When the Omega Pirate is defeated, it collapses onto Samus. The Phazon inside its body infects and transforms her Gravity Suit into the Phazon Suit. This upgrade protects Samus from ordinary blue Phazon and is essential for surviving the final stages. It also gives her access to the Phazon Beam, though that weapon is usable only briefly during the final battle with Metroid Prime.

Thardus and Flaahgra are earlier bosses, while Meta Ridley is fought much later, immediately before the final encounter.