Phoebe had never shown Kate everything she had. When she'd arrived, it had been confusion mixed in to everything else emotional she had been going through and then later with their occasional sparring, she had always been conscious of her strength. They were probably evenly matched with Kate going up against Abnormals and Phoebe always facing demons, both enemies were stronger than humans but Phoebe had never used her full strength and skills with Kate, not wanting to hurt. Like a strong man never using their full potential, always conscious of the ability to hurt.

But with Kate's snarl, Phoebe took the gloves off, figuratively. "You want a fight, you got it." She would still probably get her ass kicked but they'd both have a good fight and Kate would get her aggressions/frustrations out. Phoebe attacked with a kick toward the ribs.