I feel my question is really basic, so let me know if I missed a FAQ somewhere.

My house has multiple ethernet/RJ45 ports in all rooms AND multiple phone/rj11 ports in all rooms. These are completely separate in all ways.

My network provider came into the house and they gave me a router/modem that I installed in a room. Now, reading this sub I understand that I can buy a network switch, connect it to the router and then connect on the switch all ethernet cables (either with a patch panel, or keystones) to the switch to share the internet to all rooms. That is great.

But what is the equivalent process for the telephone? The router/modem also offers voip and a phone device is connected to it and I have a single phone there. But ideally I would like to share this phone line to all other rooms that I can use a landline phone not just in the attic (where the modem currently sits)

What device do I need to buy that takes an rj11 jack/phone line as input and shares it to other rj11 cables?