I mean, he’s also is ridiculously powerful.

Potential way it could have gone down if both entities were less cordial:

Spirit: “I could curse you! Samurai twice as large as you have wept at my feet!”
Phil: “Just Samurai? No Shinto shrine maidens or Buddhist Priests? So… how powerful was the most powerful entity you can curse?”
Spirit: “I… well, I’m a spring spirit, so basically anything with less dominion? A spring is about the size as a shrine, so I could probably curse even a full head monk if he came into my territory!”
Phil: “Could you curse a Fox Spirit or an Angel?”
Spirit: “Oh are you $#!77ing me? That’s like asking a Sergent if he can take on an entire platoon by himself.”
Phil: “I’ve straight up wiped out an entire legion of angels.”
Spirit: “I.. wait, you can’t…”
Phil: “Even and especially war angels. Silly ones, shaped like weapons?”
Spirit: “You saw them and liv…”
Phil: “It was almost accidental. They’d just pop out of nowhere, then kneejerk reaction, then *poof*.”
Spirit: “Uh…heh…”
Phil: “So then to try and make nice, the celestials sent a 9-tailed fox spirit, Yuki, is her name, by the way, to try and ensure they were on good terms with me, because they were worried their constant attacks on me might cause me to go to war with them, and wipe out the entirety of the heavenly hosts. But thing is, I wouldn’t have because their attacks barely registered as anything more than an annoyance.”
Spirit: *thinking he may have bitten off more than he can chew*
Phil: “So… you can try your curse if you want. I’m honestly curious if it’ll even tickle.”
Spirit: “Okay, sorry, no disrespect….”
Phil: “Seriously, try it. I want to see what it looks like.”
Spirit: “Um… okay, since you insist…”
*poof*
*Phil turns into a girl and is wearing a maids outfit*
Phil: *Grinning* Wait, some magic actually worked on me?!? I get to experience magic!?!
Kate: “That particular kind of situation does tend to be a particular weakness of yours… not that I’m complaining. Just don’t sneeze or you’ll dismiss it.”
Phil: “Why do you think it worked?”
Kate: “Might have something to do with those dreams you told me about? The Null is *kind* of a Magi, maybe those dreams were your Null Spirit telling you that you had an exception?” (In reality it’s because of reverse-plot armor that causes Phil to end up in maid outfits, and that is fantastic.)
Phil: “Oooo, I get to feel magic! It’s all… tickley, I like it!”
Spirit: “What is happening?”
Phil: “Hey, any other curses you can do!?! I want to see what they feel like too! You’ll stick around, right???” *she gets all sparkly-eyed*
Spirit: *sweatdrops*