Mail app stopped updating from Yahoo account

Try to delete and readd the account. That usually fixes a lot of email issues.

If you can’t send or receive emails on your iPhone, iPad, or iPod touch - Apple Support

If it's still not working try to reset network settings, because it could be that you just aren't able to reach those emails for some odd reason and your phone is going the wrong way to receive them.

If your iPhone, iPad, or iPod touch won’t connect to a Wi-Fi network - Apple Support

One of those two should fix it, in most normal circumstances especially since your other things are working.

To Sync mail from more than a week ago with your particular mail account you could try the following which is to change the Mail Days to Sync.

On your iPhone got to Settings > Mail > Accounts and under Accounts select (tap) the Yahoo account you have the issue with.

Now down towards the bottom will be Mail Days to Sync tap this then adjust or tick your desired amount of time with the maximum being No Limit.

Then go to the Mail app and check your emails.

I'm having the same issue. Did you ever get it resolved? Argh....