[mr. tegu]

Does your boss think you guys are buddies? If so, he may not think he is asking you to do anything that bad.

Also, it sounds like you only verbally expressed your disagreement about firing him over the phone, not firing him in general. If your main concern was the act of firing him at all, that should have been what you expressed, not the whole phone thing. For all you know there is more to it and he deserves to be fired so if you say you aren't sure he should be fired perhaps your boss could explain why he should be fired.

Then if its still clear he has to be fired and that there isn't a great reason beyond what you described, say you think that it should wait until after the holidays.