1st phase:

Luneth - Red Mage
Ingus - Warrior
Arc - Monk
Refia - White Mage

I haven't reached the fourth phase yet, and my characters are level 39 and I'm at the part where you gotta wake up Unei.

2nd Phase:

Luneth - Red Mage
Ingus - Knight
Arc - Monk
Refia - White Mage/Scholar (Hein battle)

3rd Phase:

Luneth - Red Mage
Ingus - Dark Knight
Arc - Dragoon
Refia - White Mage