So, Phillip's skill 2 without EGO is likely sunset blade, as it is a series of 3 swings from different angles. And his skill 3 is clearly Stigmatize, the only page unique to his base form in the Dawn Office reception.
My personal guess as to how he unlocks EGO is that it would be similar to Rabbit Heathcliff's passive (building up a status and then getting resonance.) Stigmatize in Ruina was a page that granted a negative emotion coin on use, so it'd be cool if he had a unique status called Stigma that he can build up through both his passive and s3 and then trigger via some form of resonance, perhaps.