Be angry at the person leaving out "Report: " from the article in this post, not Axios. It's very clear that Axios is reporting on private conversations from its title and contents.
And their source is pulled from an NYT article, so they add absolutely nothing.
Indeed, Mr. Trump has often been in a foul mood the past few weeks. He has ranted about Ms. Harris. He has called her “nasty,” on “Fox & Friends,” and a “bitch,” repeatedly, in private, according to two people who heard the remark on different occasions.
You know that's how much of journalism works, right? A single outlet will break a story, and then other outlets will report on that story, citing that original outlet as the source. They directly link to the NYT in the Axios article.