The Phazon Suit is a suit upgrade in Metroid Prime that allows Samus to travel through phazon without getting hurt. It also allows the use of the Phazon Beam, which is is needed to defeat Metroid Prime. The Phazon Suit is acquired by defeating the Omega Pirate.
In Metroid Prime's 100% clear ending, a brief cinematic is depicted of a hand forming out of the remains of Metroid Prime, having absorb parts of Samus's discarded Phazon Suit. This being would go on to become Dark Samus, a major antagonist of Metroid Prime 2: Echoes and Metroid Prime 3: Corruption.