iPhone contacts messed up in Share menu

This is a strange one. Apple's official solution was "update your iOS," which 1) didn't work and 2) told me they had no idea what was going on.

I have a few contacts where sharing from the Share menu causes the phone to manually add a country code that's incorrect. That causes the message to go as SMS (green text) to a number that doesn't exist.

I can solve this by selecting Messages instead of the contact's name in the Share menu. But that gets old, as one of the people this happens with is my wife, so several times a week I try to send her a photo and it doesn't work. The same issue happens with her trying to send me photos, links, etc. from the Share menu.

I think this is because, although we live in Europe, we spent several months in the US this year, and a setting was changed based on our location. Or something.

And screen grab showing that somehow the phone added a 011 to the number:

I found the Dial Assist option in the Phone settings, which automatically adds a country code. I was excited. But when I turned this off it didn't change anything.

I've also deleted the contact, then manually re-added it. No change.

Anybody have ideas?

[Edited by Moderator]