Contacts and Phone on iPhone think I'm in a different country

Yesterday I got a call from my wife and the iPhone said "Maybe Mrs. SSteve". The phone number was the international version of a U.S. phone number and her custom ringtone didn't play:

Voicemail is also showing international versions of U.S. phone numbers and also shows "Maybe" (normally it just shows the name and no phone number at all):

Contacts isn't formatting phone numbers at all:

Contacts on my iPad still formats numbers the way I expect:

I'm running iOS 12.3.1 on an iPhone 6. I remember seeing recently that there was a carrier update. I must have installed it because Settings -> General -> About doesn't show an available carrier update.

I tried iPhone Contact List Default Country Wrong but dialing *228 says the number isn't allowed.

I tried setting my Region in Settings -> General -> Language & Region away from United States and back but that didn't work. Where else does iOS get the region for phone numbers?

When I was writing this question and was in Language & Region, I tried setting the iPhone Language even though I didn't expect it to do anything. It was already set to English but I went ahead and selected "English (US)". It went to a black screen that said "Setting Language" (or something similar) for a while and when it was done all the phone numbers are displaying correctly. So I guess it's possible the language wasn't set to "English (US)" but I can't imagine why. Anyway, since I already went through the effort of editing the screenshots and writing the question I figured I'd leave this here in case it's helpful to someone.