Well several things. It's wisdom based casting, so you get the good perception and will saves from that. Phantom weapons can be anything you want. Also you have access to a different spell list. This is probably a downgrade, but the spiritualist list does have healing spells which is something that magi lack. Also you can cast in heavy armor from level 1 so your AC can be high right from the start
There's a guide specific to the phantom blade floating around. I don't agreed with everything in it but it does have some good thoughts in it.
Also if you are looking at phantom blade consider taking vmc magus. Because you have spell combat you can be excellent use of magus arcana that usually only work for a magus proper.
|Chromantic Durgon <3|
I’d say the spell list was more of a side grade
The Spiritualist is less blast but it still has good offensive options for touch spells (striken heart and vampiric touch for example).
But also gets better utility with things like breath of life and heal and so fourth.
The main issue for me is that combat casting is very difficult with psychic casters and whilst phantom blade do get an answer for it, said answer doesn’t really become useful till level 12.
You get ethiric focus at level 4. From then on you are pretty much good to go, though you do give up your swift actions.
For a single character that can cover a lot of bases I really like the phantom blade. You get the action economy of a magus with healing spells and you have spontaneous casting which I personally like. Though to be fair spontaneous casting doesn't pair as well with spell combat because you can't really use metamagic with it very well.