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?
You could connect that port to other wiring as needed to connect to multiple telephones. You don’t need any special device to do that, you can just daisy chain wiring, or you can use an analog RJ11 phone splitter, such as something like this:
https://www.amazon.com/LORJE-Telephone-Splitter-Multiple-Modular/dp/B006ZASX26
You could plug that into the telephone port on the router to get five jacks, and then use short RJ11 cables to an existing RJ45 patch panel to distribute from there to ordinary RJ45 jacks in your home.
RJ11 plugs will easily plug into an RJ45 jack.
Just take care to make sure that you know which jacks are which - don’t directly plug between an Ethernet port on a switch or PC into an analog phone/line or vice/versa.