from the admin manual, to save others the hassle of finding this info:
When the device is operating in router mode (OBi202/OBi302 only), the built-in web server may be accessed from the LAN
side or the WAN side. While access from the LAN side is always allowed, for security reasons, the access from the WAN side
may be disabled by configuration. In fact, the WAN side access to the web server is disabled by default. You can enable this
option on the device web page (from the LAN side), or by using the device configuration IVR (* * * 0 option 30) from an
attached telephone.