The talk show host has taken what the caller said out of context by shouting over him. The caller said that it was an unanswerable question because this contentious individual gave him a loaded question. Setting the question up as if you believe in the necessity of going to the temple, then you are not a Christian.
The answer to the question is this: Yes you do need to go to the temple to enter into the Highest Degree of Glory within the Kingdom of God. You do not need to go to the Temple in order to enter Paradise, or Heaven. And finally yes, Mormon's are christians, because it is only through grace that you can obtain this Highest Degree. There is nothing in the Bible that would indicate that in order to be a Christian you must believe in unconditional salvation. The Bible clearly points to conditional salvation when it teaches that: Faith without works is dead, and he who is baptized is saved, but he who is not is damned.
So in short you have to live by every word that proceeded from the mouth of God to be saved. Not just those that you find most convenient.