0815dela,
In the Obihai OBi202 published example you reference the example is using a separate router contained in the OBi202 to communicate with the IP Phone. The example is using an IP Phone connected to the OBi's LAN (not the internet) port. The IP Phone is getting it local (OBi) network ip address by DHCP from the OBi. The OBi202 is connected to the internet (thru the Internet port) and the OBi202 gets it own ip address from the internet server (or from external router connected to the internet server.
There are configuration settings on the OBi202 for both the WAN (internet) network and the LAN (OBi local) network. On the LAN (OBi202) network you can enable or disable DHCP. The local network ip address is also configurable.
The example is also using a Proxy Mode feature on the OBi202 which allows the sip phone to register to the OBi202. This feature is only available on the OBi202 (and OBi303) and is described in the OBihai Admin manual.