i suppose, depending on which version of PHP you have, as in CGI or the Apache Module, you can control what PHP runs as...
but... assuming Apache runs as root (which it does on *nix boxes i have sites hosted on), i would assume that the PHP module version would run as root as well, however just because it runs as root, does NOT mean it has ALL permissions available to it, that can still be set by directory...
now, the CGI version, i'm unsure of, since i never use that version, but that is essentially a separate process runnning, so that "may" run as web, apache, or another group.