Dialed phone numbers are in the wrong format (international, should be US)

My iPhone now dials in international groups until the phone call is in process and then it swaps back to US format: (123) 456-####. I didn't change any settings and it is hard to tell what I am dialing now because I'm looking at ## #### #### instead of (###) ###-####. Why did it change without my doing anything and how do I change it back. It is very confusing to look at.