The fight is pretty hard to learn as a Black Mage for sure, but its rewarding since you can output as much damage as any other DPS at the end, even though some people think Black Mage is bad on that fight. Use Sharp Fire as your ally for progression until you feel comfortable on mechanics to Sharp Thunder. If you wanna help your healers you can also use your untraited Virus on EDD.

Adding to what Alayna said, you can also Manaward on last phase's start so you can position yourself closer to the center taking the same damage from GA-100 as your party and position yourself to the upcoming Optical without even moving or giving your healers a headache.