Grinding old levels for item drops is your friend. Also, I didn't figure out for way too long that when you're in Solphie's stomach menu, you can click arrows to go to a different menu and feed her some of the summoned units you don't want to level her up - something that REALLY enhances her. And if I'm not mistaken, it enhances your telekinesis too.
Later fights got a whole lot easier for me after that.