PHPoC itself has a webserver to provide a web interface. When receiving a HTTP request, it executes the php script in the requested file (if there) and respond to the client. Webserver is independent of PHPoC main script. TCP 80 is used for web server and you can use the interface via Internet Explorer, Chrome or any other web browsers.
To use the web interface, "index.php" file should be in the file system of P4M-400. Connect to this page by entering device IP address after connecting it to network.
If the name of file is not "index.php", just specify the name of file after the IP address with slash mark.
Since the web server executes the php script in the requested file, user can put php code in the requested file to interact with peripherals such as I/O port, I2C, SPI, UART, ADC and so on.
It is worth noting that there is other way to interact with the peripherals in real-time from web interface. This can be done by using websocket.