Even if he did end up in a psychiatric ward, which I don't believe he did, Phil would get himself discharged relatively quickly. I think the doctor reviewing his case and interviewing him would quickly recognize him as an instance of moral insanity rather than anything treatable; a lost cause, if you will. He isn't a raving lunatic, or at least he isn't when it's important not to be, as I understand it.
Phil's problems, while psychological in origin, are not the kind that a simple "medicate and release" program would be able to deal with: people with more complicated illnesses have to come to the understanding that they need help beyond medication and actively seek it out, which Phil will not do. Committing him is likely not possible since, I can tell you, having seen long-term committal patients during visitations with a friend who ended up in the hole, Phil is not that crazy. Not yet, anyway. Give it time.
However, he would likely be held as long as possible. Certainly longer than three to seven days or whatever he claimed. As I understand it, there's a date they have to release you by--usually 2-3 weeks after you're admitted. After this they have to either let you go or hold a hearing to formally commit you. California (I think this is where he is now, right?) has all kinds of bizarre laws about everything but I think that's how it works.
Anyway, most people are typically released long before that date because they've made good with the doctor and have medication prescribed and appointments set up and blah blah. My friend's stay in the psychiatric ward lasted for about 5 days and then they let him go. Apparently he was roaming around the street tripping balls on a shit ton of acid (I don't know why and he doesn't remember, but we do know he took something like 7 hits--almost usurping my high score of

which made people think he was schizophrenic (7 hits of good acid will do that to a man). After the acid completely wore off he told the doctor it was drugs and they just referred him to NA and let him go.
In most (probably all) psychiatric wards there's a whole bunch of stuff you have to do to prove you're normal and mentally sound while you stay there. My friend told me there are group seminars/sessions that you have to go to and participate in and you have to be nice to everyone--it's basically like a junior high sped room where everybody has to rack up "points" to get candy at the end of the day or something. If you do good, they tell the doctor you're normal and he lets you go, basically.
This basically means that Phil would be in the psychiatric ward against literally everyone's will until his expulsion date. He is not a socially inclined person: he is all-around unpleasant to be around, vulgar, crude, offensive, anti-authoritarian, bitter, violently-minded, petty, obscene, narcissistic, vengeful, a total jerk with a victim complex, a whiner, a tactless piece of ham, an idiot who can't make conversation that doesn't revolve around himself and his interests, and insert a-logging here. They would have to hold him until either the doctor just discharged him to get rid of him or until his time was up, at which point it would long have been clear that Phil is just a huge, whiny jackass with no respect for anyone, including himself. That would probably last at least a month.
So obviously he didn't go to the psychiatric ward.
@AnOminous the blotters my friend got around that time were about 150 micrograms each, so he had over 1000 ug of acid in him. That's objectively a lot of LSD.