Because a phishing page is basically just a mirror. No successful phishing can really occur unless you provide the page with information, though, so as long as you don't fill in any forms or download any weird applets you should be okay.

(The linked URL was, when I checked, a legitimate and non-malicious mirror of the original.)

EDIT: Obviously a phishing page is not a proper mirror - but they both share the attribute of being very similar to another page, and with "name.tld" as a sub-domain it makes sense that a browser might incorrectly label a mirror as a phishing page.