You can't, because I don't think Microsoft account lets you import from Yahoo
But I believe you can export from Yahoo to Outlook. So you can try to export your contacts from yahoo to your hotmail/live/outlook account you are using for your phone.
1) Go to mail.yahoo.com > contacts tab > click on the actions tab with the gear icon > export all > microsoft outlook. It will download the file to your computer. Make sure you know what name the file is being downloaded to and where. It should be named something like yahoo_ab.csv
2) Go to outlook.com and sign with your account (again the one you are using for your phone). Go to the people tabs > import contacts > import from file > Microsoft Outlook (CSV) > chose file to import >find the .csv file from your computer > import contacts
It should automatically update in your phone once the new contacts has been added.
If not then go to your phone, Settings > emails and accounts > Microsoft account (the same hotmail account) > sync >contacts
See if that work
Sent: Friday, February 15, 2013 1:22 AM
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Subject: Re: How do you import the contacts from Yahoo mail into the 8x? - Re: How do you import the contacts from Yahoo mail into the 8x?
Re: How do you import the contacts from Yahoo mail into the 8x?
created by yankees in 8X by HTC - View the full discussion
Message was edited by: Verizon Moderator