1) Use the shielded cable to make two cables: one has a phono plug on one end and a microphone plug on the other end. The other cable has a phono plug on one end and a 1/4 " phone plug on the other end. Determine the microphone connections and plug from your transceiver manual.
2) Connect these two cables from the remote box to your transceiver. Use the red phono plug for the microphone. Also, unplug the telephone from the wall jack and plug the RJ-11 connector from the cordless phone base into the remote box.
3) Temporarily disconnect the microphone cable and connect a pair of headphones into the red microphone connector on the remote box.
4) Turn on the radio and the telephone. You should be able to hear the radio audio on the telephone and weak audio on the headphones. Make sure R1 and R3 are adjusted for maximum volume. Now adjust R4 for a null in the audio that is on the headphones.
5) Reconnect the microphone to the red phono jack and adjust R1 and R3 for proper levels of audio to and from the telephone with your transceiver audio and microphone controls in their normal positions. Also, adjust the VOX settings for proper operation.