The first problem is that they get spell combat as per a magus. i.e.: '...while wielding a light or one-handed melee weapon in the other hand.' If your GM says that the words under the archetype, 'A phantom blade can cast spells and wield her phantom weapon at the same time.' override that then it could work, if not then losing both spell combat and spellstrike makes this unworkable IMO.
Assuming it does work then you've got 3/4 BAB, a self-enchanting gun which you can add more properties to from 5th level, a few bonus feats and spell combat with the spiritualist spell list. That list isn't ideal for a ranged weapon user but there are a few good tricks like twilight haze, etheric shards, flight & invisibility spells.
For feats you need firearms proficiency first and point blank shot, precise shot & rapid reload ASAP. It might be worth dipping a level in gunslinger, spellslinger wizard or some other class/archetype which gets proficiency and some other useful tricks. Deadly aim and rapid shot to follow and probably clustered shots at some point. If you plan to use unarmed strike + spellstrike you'll probably want weapon finesse.
It doesn't look amazingly good to me but it has some strengths. I'd prefer to start at at least 3rd level to have the basic feats down.