iPhone not Showing New Mail using att.net

I'm a computer professional with 40+ years of experience. My wife has an iPhone 15 Pro, latest IOS. For weeks now she's been complaining about not getting emails on her iPhone, but they show up on her iPad. I spent a week on the AT&T forums until I got to the point that I'm positive I have the proper settings for their servers on her phone. They have a web interface to their email, and we can login to that and see emails there, which are also on her iPad Pro, but not her iPhone. Therefore I think it's an iPhone problem. I triple checked the normal settings on the iPhone and iPad, and they are the same. I just went through the exercise of deleting the mail app and then reinstalling it. Nothing changed, there are still missing emails.

What can be causing her to not see her att.net emails on her iPhone.