It hasn't yet -- not like Ruby, for example, with its happy Heroku. But why not?
Here's why, says Phil:
The main reason for this is that for a long time PHP didn't really need it. If you look at Ruby it is much more low-level than PHP and it needs a little kick in the right direction to become a web-ready language. It needs WeBrick/Thin/Shotgun web-servers running to get it accepting HTTP requests and is in general designed more for long-life processes while PHP has always been more about distributed .php files running once on fire-and-forget mode using CGI or mod_php. In general Ruby systems take a bit more work to get running on the web, Heroku helps speed that all up.
But this doesn't mean that PHP won't benefit from cloud hosting; just that it doesn't need it as much as other languages, not designed as explicitly for the web.
Besides, PHP apps need the ease-of-deployment that cloud hosting offers, just as much as apps written in any other language.
For these and other reasons, and based on his experience with these two beta cloud providers, Phil predicts big things for PHP on the cloud on 2012. Not only for the reasons I just mentioned -- he even observes, astutely, that the general benefits offered by cloud hosting might even be magnified for PHP apps.
To read Phil's full take, check out the full blogpost. Interesting to keep in mind for the coming year.