Advice for fighting Gael as a Caster

I beat Midir and half light, and am fighting Gael. I tried using Crystal Soul Spears and got him down two thirds health, but my problem is it burns through FP so fast. Most of the advice I found on fighting him is for melee builds. I’m at level 115 with 55 INT and a +10 Court Sorcerer staff. What spells/strategy may be the most effective?