So much for our leverage

(A Manticore demon shimmers in and hits Paige. She flies across the room. Phoebe throws the potion at it and vanquishes it. Paige groans. Two more Manticores shimmer in behind Phoebe and hit her, sending her across the room. They walk towards the girls. The creature shimmers in and attacks the Manticores. The creature reaches into one of the Manticore's chest and rips his heart out, vanquishing him. He turns to the other Manticore and it shimmers out, leaving a puddle of green blood on the floor. The creature walks over to the playpen.)

Paige: Phoebe, get the vial.

(The creature picks up the baby. Phoebe grabs the vial off of the floor and throws it at the creature, hitting his shoulder. He roars and shimmers out.)

Phoebe: So much for our leverage.

What does "so much for our leverage" here mean?