There are no error messages or bounce back emails. The iOS native email app just stops working 1-2 hours after the account is added to the phone. It acts like it's sending email. It acts like it's checking email. But new messages that are clearly sitting in the inbox (as visible on the web client) don't download.
This is ONLY in the native IOS 14+ email client. 3rd party email clients on the iPhone work fine with this very same cox.net account so I'm assuming the problem is on Apple's (or possibly Verizon's) side. I've opened support requests with them.