To connect the Gigaset Comfort 550 HS Duo to your Brovi 5G router (model H155-381), which does not have a telephone socket, you need a base station that supports VoIP and is compatible with DECT/CAT-iq-capable routers. The Comfort 550 HX handset is compatible with all DECT/CAT-iq-capable routers, such as FRITZ!Box or Telekom Speedport, and can also be connected to a suitable Gigaset IP base station that supports VoIP.

As your Brovi router does not have an analogue telephone socket, you cannot connect the handset directly. You need a Gigaset IP base station (e.g. Gigaset IP BASE) that is VoIP-capable and supports the handset. This base station connects to your router via LAN and provides telephony via the Internet (VoIP). The Comfort 550 HX handset is compatible with the Gigaset IP BASE.

Summarised:
- Use a Gigaset IP base station that supports VoIP (e.g. Gigaset IP BASE).
- Connect the IP base station to your Brovi router via LAN.
- Register the Comfort 550 HX handset to this IP base station.

This allows you to use the phone with your 5G router without a phone socket.