My best farming choice is Tritoma. She can deal with everything in one turn and her 3 turns of buffs are just enough to deal with any phase change.
In the precise case of phase change bosses, I think "until subjugation ends" are great to synergize with turn 1 attackers. While turn 1 girls do their jobs, the others stack buffs. And on the phase final boss, these girls came strong enough to handle the fight past turn 1.
Anyway, even my hard Tritoma nucker team take too much time on the 6* core stage. Too many guts.