Firstly, do you have broadband? I'm guesing not but I've asked just in case. If you have is it self install with micro filters or engineer installed with a single fixed filter on your main box?
Presuming you havent got broadband then panny300 is pretty much right.
There is no reason why you cant have 2 master socket on the circuit so I wouldnt worry too much about that. Is the socket in the bedroom a split frontplate one, basically can you remove the bottom half of the socket front?
Ideally, to comply to regulations you should run the extn from the other socket not the junction box but u wont be the first to use the main junction box
The colour codes for the line are, blue with white band on pin 2, white with blue band on pin 5 and the bell circuit is orange with white band on pin 3. If you keep the master socket in the bedroom you need'nt worry about pin 3. If by some chance it old cable (4 core with 4 solid colours) then the colours are blue pin 2, orange pin 5, then either green or brown as the bell circuit on pin 3. Like panny300 says tho, as long as the colours match either end it'll work.
If you use the junction box then you're probably gonna need to keep the master in the bedroom coz the bell circuit wont have been backfed from the main socket in the hall to the junction box.
If when you do it and you one of your phones continuously rings then reverse the wires on pins 2 & 5 on the new socket.
HTH
Steve