Yes, you can feel that your senses are enhanced around a stressful event like a bereavement. However, that does not mean that your memory of the event is accurate.
To say again, we don't replay our memories. We reconstruct them. And every time we reconstruct them they change a little. One of the things that happens is that we change our memory of an individual's actions and words to conform with our view of that person. That includes our memory telling us that they said things they never said and did things they never did.
Add to that this was a phone call. We are more likely to mishear and/or misinterpret things said on a phone call than when speaking face to face. Alcohol also affects memory, and Spencer is an alcoholic, albeit he is recently sober. The chances of him accurately recalling a conversation from 30 years ago are minimal.
So we don't need an answer for your point 1. I'm sure Spencer believes Charles said what he claims but, given the way memory works and Spencer's clear animosity towards Charles, that doesn't mean Charles said it or anything close to it. He may have done but, given the many independent reports of Charles' behaviour at that time, it seems highly unlikely.
And the answer to your second and third points is easy. Charles doesn't want to get into a slanging match with Spencer. If he made the specific statements you want, the press would have spun that as Charles calling Spencer a liar, which would have given the row legs.