Was Bolton on the phone call? If he was, he probably has first hand knowledge of what Trump said. If he wasn’t, then he is just another second hand story and as such, irrelevant.
A number of people were in on the phone call. I don’t know if Bolton was one of them. Somehow Schiff was only able to call as witnesses people who knew about the conversation only by hearsay. President Trump was aware that others were listening in...the idea that he would try to do something illegal or unethical in that situation is preposterous, but that is the theory that the Democrats have been pushing for months.