I would say that yes, the shadow dancers summoned shadow would also prevent a phantom from manifesting or cause it to retreat back into the summoner's consciousness, and I will make a note to add that later drafts.
Just a note on this before you commit, but shadowdancers' shadows aren't dismissable in the same way summoners' eidolons are. Dismissing them risks a negative level and leaves them gone for at least 30 days, so they're effectively an "always on" class feature. Adding them into this text means that three levels in a particular prestige class will effectively shut off the main ability of this base class. That doesn't seem ideal. You could honestly delete that entire paragraph from the class if you just made the spiritualist an alternate class of summoner instead of a base class (which is what it feels like anyway).