I'm sorry about the issue. Is there any error or message?
Is your Yahoo email currently working at the yahoo.com website?
Have you tried to delete your yahoo account in Settings -> Accounts on the phone, then re-add it, and check?
Do you also have a Windows XP, Vista, or 7 or 8 or 10 computer, or a Mac computer? If yes, is your email currently working fine on your computer?
Please reply at the box below. Thank you,
What is the name of the app icon you use for accessing your yahoo email on your phone, such as Email or Mail or Yahoo Mail, etc.?
Please type at the box below, then click on the Send button below to communicate with me, so I can help. Thank you,