At 8th level, and every 3 levels thereafter (13th and 18th level), the spiritualist gains a new way to use her bonded manifestation.
Do the abilities gained at later levels from the Bonded Manifestation (Su) stack, or do you have to actively choose which one is active at any given time?
For example, if my 8th level Spiritualist activates their Bonded Manifestation, would they have both the +4 AC as well as the Ghost Touch ability on their attacks, or would I have to choose to activate one or the other?
You have to choose one at a given time. At least in this version of the class.