I am not sure if there isn't some confusion, so I will try to clarify that first.
Our main product - QuickOPC - is a tool that makes it easy to embed OPC client functionality into your applications - which includes applications written with PHP. Your application, with help of QuickOPC, then connects to some OPC server that you already have. If that is what you intend to do, please download QuickOPC-Classic trial version , and when installing, select Express install for COM development. Some basic examples with PHP are installed with the product, and I will be happy to help you with further questions.
An opposite situation, i.e. when you want to develop an OPC server that somehow interacts with PHP, is also imaginable, but is not common. I would need to know more details to comprehend the needs. In such case, we have "OPC Runtime Kit", which we use to develop custom OPC servers, but it is not a product for sale as such - it is sold only as part of custom OPC development.