Connect thicker, RJ45 cord into left side of EHS box, and the thinner, RJ9 EHS cord into the right side of the box
Connect the other end of the RJ45 EHS cord into AUX port of Leitner base. Also, connect Leitner connector cord with green tape to green TEL port in Leitner base
Now, connect the other end of the EHS to the EHS port in the back of your Nextiva phone. The other end of the connector cord will go into the headset port on your phone