Well, I don't know PHP, so I can't give you specific code, but I can explain the general principle.
When your application starts you should register to Apple Push Notifications by calling the registerForRemoteNotificationTypes:
method.
When the registration succeeds and you get the device token, you should send it to your server in the implementation of application:didRegisterForRemoteNotificationsWithDeviceToken:
.
Your server should store it in some data base.
Your PHP script that sends the notifications should get the device tokens from that data base.