Alan laid it out well.
Behar Intl. Counsel 619.234.5962 Kindly be advised that the answer above is only general in nature cannot be construed as legal advice, given that not enough facts are known. It is your responsibility to retain a lawyer to analyze the facts specific to your particular situation in order to give you specific advice. Specific answers will require cognizance of all pertinent facts about your case. Any answers offered on Avvo are of a general nature only, and are not meant to create an attorney-client relationship.
I agree with Alan 100%.
Don't forget to check "Helpful" if I helped you out. This response is not intended to create an attorney client relationship and is based on the limited information available at the time of the response. Before acting on anything stated or referenced in this response you should consult with an attorney of your choosing and go over the specific details of your legal circumstances. My responses are also given in the context of the laws of the State of Louisiana. To the extent this comment involves principles of law governed by another state my comment merely reflects my opinion and should not be considered legal advice.
If you can show there are other employees who have not been terminated for using the phone or have received warning prior to termination, you may be able to prove discrimination. I would suggest contacting the EEOC if this were the case.