IMHO...
this thread/project will NOT help you..
this is for Windows.. and that being said.. the PHP (I believe) only have 1 way communication..
(ie: it can only PUSH out data to the COM port "TO" the Arduino... but can NOT receive any data "FROM" the Arduino)
From what I have read.. (on Windows) PHP is only working 1 way.. not 2 way communication.
Look around and see if you there is some sort of local 'proxy' app that will do for you (gobetweeno?) or something similar?