You are doing right, this Boss is super strong at the begining beginning and becomes weaker everytime every time you pasa pass the color Ghosts to their color vortex.
We trap It in the nord-east north-east "corner" between the EK and the RP. The rest of the team just keep passing the Ghosts over their vortex.
Eventualy Eventually the Boss starts acepting accepting more and more damage. Don't desespere!disappear!