Please note this list is still being refined and may change in places.
Origins
During the 22nd Founding the Star Legion chapter was created. Their Fortress Monastery was built on Duraan, a fuedal world in the Segmentum Obscurus, it's placement was ideal to help protect Port Maw and the numerous populated systems nearby. Duraan was a world of varying terrain, much like Terra was once, from arid deserts, to humid rainforests, to the icy extremes of the frozen poles. It enabled the Star Legion to train in all manner of environments and it's fuedal population was perfect for providing new warriors. With such a solid start it was no suprise that the Star Legion soon became known as anincredibly flexible and efficient fighting force, their exploits rapidly becoming famous throughout the Segmentum. The sight of their dark green armour brought terror to the Emperor's enemies and respectfull fear to his subjects. However such a speedy rise to power would not be noticed by the Imperium alone.
Despite recent Chaos raids, with the Star Legion so utterly in control of their assigned systems, the Imperial Navy lessened patrols in the area, instead diverting their ships to the more over stretched areas around the Eye of Terror. Seeing an opportunity to strike an awesome blow to this new bastion of the Imperium, the renegade Word Bearer Lord Mephistopheles, aboard his Hades class Cruiser "Hated Foe" travelled directly into the Duraan system and launched a most unconventional attack. As the Comet KLY78i was making it's once every 7000 year pass through the Duraan system, Mephistopheles' ship emerged from the warp and fired a monstrous broadside into it. This massed barrage of energy was enough to knock KLY78i onto a new path, one that brought it on a collision course with Duraan. So perfect was his last second timing the Star Legion were unable to react.
The Comet smashed into Duraan's largest continent, shaking the planet to the core. An explosion of incredible magnitude tore the planets surface to pieces, magma burst through great rents in the planet's crust, smoke and ash darkened the skies and all life simply perished. Almost. Amongst the flaming ruins of the Star Legions Fortress Monastery, his armour covered in the white ash of his home, Master Apothecary Tyrn clambered out of the rubble. Ignoring the searing heat of the flames licking round him, he searched the ruins for other survivors. Weeks went by as Tyrn relentlessly brought together all that remained of the Star Legion. Only stopping when the flames had utterly consumed the rubble. In total forty three marines emerged from the flames, all of them covered in the ashes of their world, the ashes of their brothers. Standing atop the ruins his armour almost entirely white, mere patches of it's true green showing through, Tyrn roared "We are the reborn! The Phoenix from the flames!"
All this time the planet was changing. Endless electro-magentic dust storms swept over the now rocky, desolate surface. The seas constantly boiled as incredible heat vented from the torn sea bed and the air was thick with dust and toxic gases. This once fertile planet had become akin to hell. Yet despite this new hell world, Tyrn and his "Phoenix Warriors" vowed to remain on Duraan, they would somehow rebuild the chapter and take vengeance on the murderer of their world. Their armour newly painted white to represent the ashes of their brothers and green to remember the Star Legion, the Phoenix Warriors began the slow task of rebuilding a destroyed world.
Home World
Many thousands of years have passed since the Death of Duraan, yet the planet has changed little since then. It's rocky surface is bleak and desolate, racked by unending dust and ash storms. Giant volcanoes are dotted over the surface, flames spit out of cracks in the ground, while great rivers of lava churn their superheated contents across the land.
A few of the human tribes on the smaller continent survived the Comet's strike and have become the source for new Phoenix Warriors. Their lives are brutal affairs, the tribes are always at war with each other and just surviving on Duraan is a battle in itself. No plants will grow on Duraan, the people have to dig out foul worms from the earth for food, a disgusting yet nutritious diet.
Combat Doctrine
The Phoenix Warriors are now an active chapter approaching the 500 marine mark. The events on Duraan's have drastically re-shaped the chapters methods. Land Speeders and Jump Packs are utterly useless in the storms of Duraan, instead the Phoenix Warriors built wheeled Buggies to travel the rocky terrain. These constant storms also make visibility incredibly poor , so bad infact that the Phoenix Warriors have no use of long range weapons, they simply couldn't be fired with any accuracy. Because of this their forces are based around close to medium range combat, advancing quickly and attacking with devestating short range weaponry and assaults. The fires of their 'rebirth' and the state of Duraan has had serious effect on their choice of weapons, other than Bolters they now only use Flame or Melta based weaponry, let their enemies burn as they once did.
Organisation