As a longtime psychedelic traveler with quite a bit of knowledge on the subject, let me clear some things up.
Phil was most likely trying to either robotrip or abuse "painkillers", both of which are typically very pleasant experiences and are frequently engaged in. However, because he is a stupid retard, Phil does not realize that 1) Motrin PM is not cough medicine, and 2) just because it kills pain and makes him drowsy does not make it a painkiller he can get high off of. Personally, I think the second option is most likely since he's tried to get painkillers before and is a complete idiot, so it's plausible that he would want what he thinks are opiate-like drugs and would mistake motrin for one because... Phil. But we won't know the truth unless he tells us.
More to the point about what happened is that Motrin PM contains two ingredients. One is ibuprofen (advil), which is typically regarded as preferable to acetaminophen (tylenol) when mixed into painkillers and cough medicines to deter abuse. Ibuprofen in large doses does far less damage to the body than acetaminophen. Neither of these ingredients are psychoactive.
The other ingredient in Motrin PM is diphenhydramine, which you will all likely know as Benadryl. Diphenhydramine is an antihistamine which in low doses can help with allergies and nausea, and can also promote sleep. Most PM substances contain diphenhydramine to make the user sleepy. As I said, in low doses, diphenhydramine is quite harmless and is generally a very useful, multi-purpose drug. What most people don't know is that in high doses, diphenhydramine is a very powerful deliriant.
A deliriant is a specific class of hallucinogenic drug whose effects resemble those of delirium (hence the name). It's difficult to describe the experience to someone who hasn't actually used one before, but for the most part these trips are terrifying. During these experiences, you often cannot tell what is real and what isn't--the hallucinations are vivid and real, and your brain can't tell the difference between them and life. Deliriants often induce paranoia and even terror; the user's mind will frequently become trapped in loops of thought, and they will generally make you stupid as hell while you're on them.
To make matters worse, deliriants tend to be quite toxic at high doses. To give you an idea of exactly what kind of stuff we're dealing with, the most well-known deliriant is jimson weed. Most psychedelics users avoid the whole class, and diphenhydramine tends to be a pretty hardcore trip even for experienced psychonauts. If Phil's "dizzy" comment wasn't just a stupid rhyming thing, then he probably took enough to experience psychoactive effects.
And if Phil is high on a substance that causes artificial delirium, no wonder he got arrested. He's already violent and clueless enough normally; just imagine him if he can't get his bearings, thinks the universe is about to unravel, has become violently paranoid and lost all inhibitions, and is hallucinating weird shit that he thinks is real.
Of all the things he could get high on, it was this. It obviously wasn't a suicide attempt; he only posted about this because he got in trouble and is butthurt about it. But he's like some kid who sniffs paint because he's such a loser he can't find a weed dealer. I honestly think that's the only reason Phil doesn't do "real" drugs--he has no friends, is an idiot and a coward, and would shit himself if he tried to ask a black dude to sell him some coke or something. So, he limits himself to stuff that's even worse than the stuff on the street; the stuff they literally are comfortable selling in stores because only a few people are ever dumb/adventurous enough to abuse it.
What a fucking idiot.
