Phantine was a planet. But Phantine was also more than that.
Phantine was a very interesting place. People could only live on the tips of ancient spires, and mined the gas and vapor-mills for fuels important to the Crusade war effort.
It was also one of the hardest wars the ghosts ever fought, and our first purely air-deployed engagement. We deployed off giant drogues and dirigibles. You would have marveled at them. I can find pictures in the library, if you'd like.