One of the things that scares even the Corsairs is the threat of a Mox bombing of Crete which would wreck havoc on the fragile ecosystem. They've seen what happened on Cambridge and so provides a small amount of assistance in order to avoid a costly confrontation. Remember: Crete is fragile and one of the reasons why the Corsairs wanted to take over Rhienland was to get access to greener planets.
The Corsairs really don't get or care about the Phantoms as much, as the active Phantom roster is usually bellow ten and they don't fly very many capitals. My -personal- character hates aliens and thus sometimes gets in fights, but generally the Phantoms are left alone because there is nothing to gain from shooting them, and so much to lose.
Generally, my contact with the Phantoms goes thus - dock and get what you need and get out. Guarded neutrality essentially.
"The thirteen saloons that had lined the one street of Seney had not left a trace. The foundations of the Mansion House hotel stuck up above the ground. The stone was chipped and split by the fire. It was all that was left of the town of Seney. Even the surface had been burned off the ground.
Nick looked at the burned-over stretch of hillside, where he had expected to find the scattered houses of the town and then walked down the railroad track to the bridge over the river. The river was there."