Cox/Yahoo instructions for this process have been practically non-existant. Thanks for the link! I'm trying it out with the iPhone atm. Removed Yahoo account and added POP3/SMTP account using the app password. It looks like the last 3000 messages are downloading, or are trying to download at least. Mail seems to stop downloading when the phone locks, and I do not see anywhere where I can set all messages to be downloaded instead of just the last 3000.
This transition has not been smooth, and tech support reps seem shocked when we express disappointment at the removal of a key service feature. It seems they've been told to tell us that email was just a "perk" or "bonus" of signing up for Cox Cable Internet.