Can you turn off the switching that happens when you are on a call? If, while on a call you pull up contacts after a minute or so it automtically flips back to the phone screen?

While on a call, I am renewing a perscripton. I have the prescription number in my contacts. Is there a way to actually dial the number that is stored in my contacts? Can you highlight the number and somehow have it dial? Copy and paste to the phone app does not dial the number.