I'm not finding much info on phantom builds, but what little I do find is rod only.
Converse with fellow players
The Phantom's build regardless of your weapon is largely the same in terms of the skill tree so the guides you are looking at are likely very close to what you are looking for as the Katana and Rod have skills that definitely to make them suffer (Lord of Thorns) to play with. In addition to this I would skip skills like "Phantom Time Jellen Plus" because if you are playing with the Rod or the Katana you may rarely get to use Phantom Time at all (let alone build Phantom Marks quickly without the aid of techniques or the Rifle) so I would also avoid Mark PP Recovery and Mark Heal unless you had extra points left over.
For the most part the Phantom's Katana is very straightforward as everything is to prioritize Folterzeit -> Folterzeit -> Third Normal attack. Everything else is either for utility/positioning or to get you into the position where you can repeat that combo as much as possible.
Azelyra's video gives out some advice for katana starting at the 35:25 mark that you may find helpful.