I believe Terence is referring to naturally-occurring molecules here. Certainly, a chemist could synthesize any number of 4-O-phosphorylated indoles, but that would reflect nothing on the chemical-producing genetic instructions of said chemist.
The argument Terence puts out is that because it's such a rare molecule, there must be something special about these mushrooms. He's also quoted as saying he puts out the argument that Psilocybe cubensis is an extraterrestrial, but that he doesn't *believe* that exactly.
Still a funny question, why do the fungi 4-hydroxylate tryptamines, while plants and animals 5-hydroxylate and 5-methoxylate? Sea sponges even 6-bromonate!