If I open a PHP file or create a new one, it opens with all three available. (CS5 Mac and Windows Vista or 7). If I open a JS or CSS file, they only open in code, but PHP will open as an XHTML until I save it as PHP, and even then it still opens in whichever mode I last had it opened.
It may be a preference that needs resetting. Perhaps someone else knows more about it.
It was a preference setting that caused the document to open in code view. Once I removed the PHP extension from that preference, a new or existing PHP document opens in code and design with all options available.
Thanks for the hint.