Exactly how are you trying to connect to it? If it's in AP mode then it will have an IP address and an SSID that the iPhone will need to scan for, but it can't use the iPhone hotspot to connect to anything else when it's being an AP.
If it is connected to the iPhone's hotspot then you need to see what local IP address the OS4P has been allocated by the iPhone and then enter that in the browser to get to the OS4P's web server.