Hey,
No worries. The puzzle is VERY esoteric. It's been haunting me for years now. I mean, it was supposed to be really obtuse, since it's technically the only puzzle in the game, but I definitely feel like I overdid it. I took it just a feeew steps further than it needed to go.
Some of the scavenger hunt stuff can be pretty hard to find as well, given how big and janky the game ended up being. I myself had to pop back into the game to figure out where the Air phrase was, which basically means I had to solve one of my own riddles over half a decade after writing it. In short, as long as you're having a good time with the vibe of the game, I don't think asking for help will invalidate your experience. I think one of the other players with a similar issue actually just ended up hacking the final door open from the files, and I honestly feel like that was a perfectly valid alternative solution.
I'll try to start off with hints, but am happy to give more direct info if requested.
The Air phrase is, as the original hint puts it, "close to home," so it isn't in the "glitched" blue city (the one that's kind of large, floaty, and ... really, really blue). It's in the "daylight" apartment area, with the diner and gallery and all that. The color blue is still very much a part of getting to it.
The Shadow phrase is, in fact, in the cave. It can be a bit tricky to spot, if I remember right. Positioning matters.
You're looking for the light phrase in the correct "region" but not quite the right spot / building. "You called for help, it came out wrong," is a bigger clue than it might at first seem. However, it is, culturally, a bit of a US centric clue, I have to admit. A bit of a Twin Peaks, Season 3 reference as well. The way to access the phrase is similar, conceptually, to the way one accesses the Shadow one.
"Gematria" is the search term you're looking for. It's a form of Kabbalistic numerology wherein letters are combined to form numbers. If I was making this game today, I'd probably have included a built in Gematria calculator in the game, but my engine/coding skills were simply not at that level at the time, so it's basically one of those "google it, find a converter online, and play around with it" kind of deals.
Hope that helps a bit, and doesn't simply cause more confusion. Again, apologies for the, um, design foibles / quirks.