I just posted on another thread about this. The only reason I came to this subreddit in the first place was because of how angry I got after watching the latest episode and seeing how ridiculously unfair everyone is towards Phil. Yeah, I know it's a comedy and its all for fun but still.
Long story short: Phil was tricked into a relationship. Sure he didn't have to "marry" Carol, but he'd been alone for two years and had no reason to believe there was anyone else out there, what would you have done for companionship?
Even when there weren't any other people and it was just Phil and Carol the two never got along. Phil (at least currently) just isn't attracted to Carol and that's that.
It's not even that he's lost his mind. Everything he's done would be perfectly acceptable in a normal situation. Granted I'm ignoring all the sitcom ridiculousness and the way the shows writing picks on Phil and makes him look like an ass.
Something you learn after being in a number of relationships is that you can't force yourself to stay in one just to keep someone else happy and you're not a bad person for wanting to move on to something that has the potential to make you happier. That's not fair to either party. If you find someone that you're more compatible with then it's perfectly ok to break things off and move on.
I know a lot of people will say "oh so you should just end a marriage because you find someone else?" and get all butt hurt about that, but that's not what I'm saying. Phil and Carol are married by name only. They've only known each other for what, a couple of weeks? Months, at the most? Breaking things off wouldn't be unfair at all. That happens in the world of relationships.
It would be different if they had been married for years and had a family but they don't. They're still essentially strangers and they were never even compatible to begin with.
Everyone treating Phil like shit because they expect him to stay with someone he clearly doesn't care about and was obviously only with as a causality of circumstance is beyond unfair.