Someone have already answered.
Php can't do that in windows; you need a php extension to have the job done in windows, that means c+zend if you want to use "full" php function.
Php_serial_class works read/write only on linux (casualty?)
If you can, better to use linux or take a look at this project on sourceforce ArduinoPHP download | SourceForge.net).
Good luck