My sister-in-law used to do this. My brother would be talking to me on phone and she was constantly chipping in, often wrongly guessing what had been said.

No wonder your husband is irritated if you keep interrupting his business calls. Business is far different from chatting to a friend/relative. You should find something else to do whilst he's on a call.

His job may depend on you not distracting him, especially if his boss is on the phone.