Phantom's Katana has a few problems compared to the other 2 weapons the class can use.
•Short range on attacks
•One truly good DPS move
•High PP consumption + Low PP regen
•Slow Marker buildup
•Awkward to use
Darkwave Agile/Lightwave Klauz remediates the PP problem on the weapon thanks to it's potential, so that's a plus.
I'd say Ph's Katana shines best in 1v1 encounters, but it still gets outshined by Rifle and Rod because they offer better and safer options. You will do well enough for most of the multiplayer content, but you will struggle more in quests where you have to fight mobs rather than bosses (such as Divide or Endless.)