Here is the Yahoo Webpage:
http://help.yahoo.com/l/us/yahoo/security/phishing/phishing-117760.html

Where they say:

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If you receive one of these emails, mark it as spam, including any messages that originate from a yahoo.com email address. These emails are usually sent in bulk, and are rarely targeted at a specific individual. Yahoo cannot investigate these scams; reporting these emails as spam is the most effective measure you can take as it will help ensure additional copies are not delivered.
===== quote end

Now if the email originated from a Yahoo member, there is also another webpage for reporting that member:

http://help.yahoo.com/l/us/yahoo/mail/yahoomail/abuse.html
Yahoo! Mail Abuse Form

But – some criminals have impersonated Yahoo email so there is no guarantee the abuse will stop.

You can also report the email to the federal government at the Internet Crime Complaint Center:
http://www.ic3.gov/default.aspx

TonyRB
Saturday, January 2, 2010