I worked in sales and was constantly on the phone and selling in person. Here are words to use to structure your logic: 

1: If you have a bunch of things you want to say, use transitions like: "in addition" or you can use "in terms of", "moving on to", and the last you say is with this transition "finally...." Why? So it looks like you are structuring you answers and it also buys you time to think a bit more! 

2: When someone asks you a question and you need a few more seconds to respond, you can repeat the question. For example, what are your thoughts on the competitive environment. "that's a great question; My opinion on the competitive environment is...."

3: If you don't know again you can say. I am sorry I don't know, but I will find out and get back to you ...write it down and then follow up with the interviewer in an email later.