Have you checked with Yahoo? Was the account previously configured on your phone and this is coming up while updating the password or is this a new login to your account on your phone?
What mail app are you using? If you say "the default one" we'll also need to know what device you're on as some manufacturers put their own on while others just leave well enough alone with the GMail app.
Also, what version of Android? If it's old enough Yahoo may be blocking the sign in for security purposes.
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