Shibalien appears as a peon until the bosses spawn.
Try to get rid of Bun Bun Symbiote quick; his Shockwaves can end your army. He is definitely the hardest part of the level. Lead him nearby your base to avoid attacks from I.M. Phace and Galactic Overseer Nyandam.
Once you kill Bun Bun Symbiote, I.M. Phace should be easy. He doesn't have a ton of health. Once you kill him, just play the waiting game with Galactic Overseer Nyandam.
Megaphrodite helps immensely in this stage.