Is it illegal to record a phone call from someone who is threatening your life over that call when you know that there is simply no time to gel a court permission to record?

First, you need to check the laws of your state: if you are in a "one-party consent" state, then as long as one of the parties to the phone call--that is, you--consent to the recording, it is legal...and by definition, if you are recording it, you consent to the recording.

If you are in a two-party consent state, then it is illegal to record without the consent of the other party. However, if the authorities try to bring criminal charges against you, you *may* have a good defense: necessity. The law sometimes justifies otherwise illegal behavior on the grounds that it was necessary to prevent a greater harm. It is not certain you would prevail on this basis, but it is at least a reasonable defense to invoke.