The "Azure SDK for PHP" link provided above (which points to the Interoperability Bridges website) has been deprecated in favour of an SDK hosted on GitHub...
http://github.com/WindowsAzure/azure-sdk-for-php
There is also a supporting "PHP Developer Center" website:
http://www.windowsazure.com/en-us/develop/php/
I did try editing the URL for the "Azure SDK for PHP" myself, but the URLs seem to be stored in a separate file which I was unable to find.