The opening sentence of "The Call of Cthulhu", famously, is "The most merciful thing in the world, I think, is the inability of the human mind to correlate all its contents." This beginning signals the reader to read not only the story but all future entries in this newly created fictional universe like a detective gathering clues. No rigid canon exists for Lovecraft's original mythos, but the reader can piece together something like a coherent cosmology and background by reading everything from "The Call of Cthulhu" onward. That the term "Cthulhu Mythos" later became the label for the constellation of lore created by Lovecraft fits well not because Cthulhu Itself is the most powerful creature in the pantheon (It isn't) but because Cthulhu's first appearance also marks the origin of the cosmology that would grow to lie beneath most of Lovecraft's subsequent fiction. The revision stories, meanwhile, possibly form their own parallel universe.
The words "Ph'nglui mglw'nafh Cthulhu R'lyeh wgah'nagl fhtagn" are described by Wilcox as an attempt to make sense of something unpronounceable by the human tongue and vocal chords. Indeed, any attempt to speak the words normally always ends up including additional vowels and/or syllables, because the human mouth is incapable of parsing the words exactly as written with normal speech. However, if one simply closes the gap between their tongue and soft pallet at the roof of their mouth and forces air through the gap, the sounds made are far better approximations of the words with exact spelling than deliberate attempts to speak them. To add a bit of Fridge Horror to this, those sounds could also be described as the "wet, slopping noises" made when Cthulhu rises from R'lyeh...
