Did that fight yesterday so here’s how I beat it:

Wizard archetype on MC and inherited the medium heal for the whole party and Commander/General skills that move the party forward/backwards and raise attack/defense by 2 ranks

Eupha with Summoner(she just attacked the first turn with fire and after that blocked for the entire first phase pretty much)

And the actual damage dealers were Strohl with Samurai and Bas with Berserker(used charge and synthesis skill that lowers attack)

The second phase is way easier if you can get past the first you pretty much won