You know, I've joked about Phil having Korsakoff Syndrome several times, but I'm wondering if there's some truth to that. Given Phil's lack of exercise, hermiting and general obnoxiousness, there's a real chance that his brain is pickled by his gin habit. Think about it: his memory troubles (exacerbated by his lying), the making up of stories, the paranoia. They're all symptoms. And again, it's all exacerbated by his echo chamber and inflexibility in his routines. It's all really sad, when you get down to it.
Reason I can't get down with this theory is that Phil very clearly loves to indulge in literally every quirk, tick, and vice he has, which means he drinks a lot because he also loves to lie a lot, over-share, project, shift the blame, get jealous, talk about poop, make racist remarks, waste his money on useless garbage, etc. etc. Everything you can think of in Phil's behavior, he goes over the top with, as much as he possibly can. And he doesn't need to be an alcoholic to be like that, either.
I have no doubt that Phil has fucked himself up permanently from drinking too much, but it isn't the reason he's a pigroach. That stems from him being the type of addict who wants to not get better, just be enabled forever. There's no way he was already brain damaged back in the early 2000s when his shitty personality started getting him a rep, and I stand confident that he was a dick in high school as well, we just don't have the stories because he more than likely held it in back then. Just as he has been holding back his racist humor for years, in direct contrast to how much he wants to let loose with it just like he does all his other habits.
Oh, and that's to say nothing of the fact that his drunkenness these days is causing the real Phil to come out and play, making him be honest. And then lie about what he said, with much indignation that anyone would dare notice that he is still Young Phil at heart. Again, cementing that he really wants to indulge in all his habits to the fullest extent, and is running problems doing so because he can't drink so much AND stave off those moments where his rep gets sent back by the n-word he clearly says off-camera with frequency. Phil is not mad that he's fucking himself, he's mad that the world isn't letting him do everything he wants, which involves way more than getting wasted.
Basically, Phil's addiction is to being an addict. It doesn't matter what his vices are, he'll always feel entitled to keeping every single one of them fat and happy until the day he dies of them. There's a reason that punishing him for his behavior never teaches him anything, and it isn't from his low IQ. Even dumbasses stop playing with fire after getting burned, unless, like Phil, they need the feeling of getting away with shit more than they hate the feeling of not getting with it.