Would it be acceptable to assume that if a person is in the psyche ward and being evaluated, they are frightened? Would it also be acceptable to assume that if someone is on the psych ward that they are not thinking clearly? Observations during this time allow him phone call privileges, so you could notify the ward that his calls are being directed inappropriately to you. They will tell him not to waste his call privileges. Whether or not he listens is another story- he is, after all in the psych ward.
Call friends and family and let them know that you will be turning off your phone and not to worry. Tell them that you are experiencing calls that you do not want to answer. Turn off the phone and make plans to get a new number. Until you can disconnect your current number, expect calls from him. Try not to answer them and become engaged in guilt. This is his battle. You are not responsible for what happens in his evaluation. Good luck.