Only worth noting if Greenblatt has denied the phone call.
E.g when Russia stopped denying the presence of North Korean troops, it was pretty much cast iron proof that Ukraine's recent videos of the prisoners were not fakes.
A denial wouldnt necessarily mean it wasn't true, but the lack of a denial is very strong evidence that it is.
Whenever the Russian government denies something like you're suggesting, I take it to be an admission. I'm usually right.
You're naive and wrong.