They actually don't. While there have been some overreaching TOSes like that in the past, most sites these days simply insist on a nonexclusive license for use.
Facebook for instance:
"For content that is covered by intellectual property rights, like photos and videos (IP content), you specifically give us the following permission, subject to your privacy and application settings: you grant us a non-exclusive, transferable, sub-licensable, royalty-free, worldwide license to use any IP content that you post on or in connection with Facebook (IP License). This IP License ends when you delete your IP content or your account unless your content has been shared with others, and they have not deleted it."
More here. They also limit that so that you can't just delete something and then instantly sue them because it's still up, or it's been shared by third parties, or you made it a public post and it's now up here on Kiwi Farms, or they used it in an ad, or whatever.
Phil is a dipshit, though. There's no way he can prove someone even read that. They may have come into the thread on the last page and have no way of knowing any of that. Usually to be enforceable, those kinds of things have to be prominently placed or you have to click through to agree, whether with a popup or other mechanism to ensure you're at least aware there's a TOS and that you're agreeing to it.