Open the socket in the bedroom, there should be two pairs of wires normally, a blue & blue white pair and an orange, orange white pair. The exact colours are not important.
Make sure one of the pairs is connected to the socket in the bedroom, if it isn't strip off the insulation and make the connection to the socket.
Go to the main socket and open it carefully, see if there is a pair connected to anything other than the socket for the main phone, this other pair should be going upstairs. Chances are that the sparks never connected the top or bottom pair or connected the wrong pair.