Phone connection for Lucent 854

Question

I purchased a Lucent 854 to use at work. When I got it I realized it is set up to connect to 4 separate lines. What we have at work in 1 phone jack that has 3 separate lines in it. How can I hook up the Lucent phone to this and make it work? Do I have to separate the 3 lines then connect to the Lucent? Please email me at [e-mail] with any help you can give.
Sincerely
Robert