Phoenix Strike launches the active charge, not all three charges at once. So if you have it built up to Charge 2, Chaos Lightning will be released.
Phoenix strike is a handy skill if you're fighting around monsters with different Resistances, because you don't need to change between skills.
Releasing one charge of Phoenix Strike results in a meteor strike; the meteor will be centered on the mob that the charged was released on and will take 3 seconds to fall. Once it has fallen, an aoe (consisting of 9 patches of fire totaling ~5m diameter) will remain in the area where meteor struck. The duration that this aoe of fire patches remains on the ground depends on the skill level.
Releasing two charges of Phoenix Strike results in a chain lightning attack. The chain lightning goes outward in a grid from the mob that the charge was released on, circles around, and then lightning paths randomly travel around an area of about 20m. In total the lightning remains for 2 seconds after released.
Releasing three charges results in the release of ~15 chaos bolts. These do cold damage and will freeze targets in their path. They originate from the mob that the charges were released on, then spiral outwards with alternating bolts going clockwise and counterclockwise. The chaos bolts remain for roughly 1.5 seconds. Freezing duration is cut by 3/4 in Hell.