I saw a lot of different things working at the phone company. Most prewire is daisy chained jack to jack.I would run a wire straight from your Network Interface, by itself. One safe room I remember is how I would do it. Of course, this is before cell phones took over.
The company owns the line up to the NWI. Customer can do what they want from there. He ran a line straight from his Interface, to his safe room, dial tone on 2 conductors. At the end of it, in his safe room, he put in a simple toggle switch. On the the other end of the switch, he sent his dial tone back to the interface, on the other two conductors, where he connected the dial tone to his prewire going through the house. This way, if something happened, he goes to his safe room, flips the switch, and only he can use his phone line. No one upstairs could put it "off the hook", or whatever.
He then very cleverly hid his interface behind some plants, our wire was already in conduit, his didn't even show.
I'm sure you'll have power in that room, I would also add a coax for your TV service.
You mentioned fallout, don't forget your iodine pills, and Geiger counter.
Since your escape hatch is only for extreme emergencies, I would build a box around it, and fill it with sand, just like the 60's military ones had. The sand is a good stopper for gamma fallout, and could be removed simply by opening the hatch, and letting the sand pour out. Just my thoughts.