How to I plug in an NBN compatible cordless phone for use with VOIP, into a DECO x-20 DSL AX1800 wifi 6 modem router?

Our old modem has a phone port (NBN modem from iiNet), however the DECO only has ethernet ports. I have the DECO working for internet but cant get our voip phone to work. I have plugged it into the DECO ethernet port using a telephone port cable but no luck. iiNet suggested I need to configure the modem with the netphone number and password, but I cant see any telephone settings in the app. The Uniden cordless phone we have is a few years old, but not specifically NBN compatible, but did work with our previous modem.

Perhaps the DECO does not support VOIP?

Any help appreciated.