Murphy's Law:
Are you here?
I do not wish to rain on your parade, you've made a significant finding.
Though from my post it is far more complex. Just as I've written here for a year, and elsewhere, that OP himself is immensely complex.
So in your finding of OP's statement "I wanted to ask Reeva why is she phoning the police is indeed telling.
And I listened and it sounds like he said "isn't.' But you see from my post above, perhaps the most important aspect is the dip in the volume of his voice [and all that that implies IMO];
But that does not detract from your highlighting whether he said is or isnt.
You are prob. right, and I speculated a year ago that the heated argument led to a either him preventing her from leaving and/or a minor assault, and whether he ended up saying is or isnt to me the dip in his voice is more important and is proof of what you are alleging.
As things escalated, at one point, she tried to call the police, and if he already assaulted her, or just imprisoning her is a crime, he did not want to face jail time. So he got the phone out of her hand in some assaulting or threatening way, perhaps getting his gun early in the scenario and pointing it at her and threatening to shoot if she did not drop it.
She fled to the loo or maybe some of this occurred in the loo, and he realized that he just committed another major crime by pointing a gun at her.
There is vastly more in my scenario.
But thanks for finding the is or isnt in re to phoning the police.
In his Oscar-speak that dip was probably telling the world what you are alleging.
In his mind, if only Reeva did not try to call the police, shed be alive. Again blaming Reeva for his killing her.
Above JMO.