How can I sync Yahoo Calendar on my phone?
There are several ways you could use to sync your Yahoo! calendar with your android device. 


Using a CSV file. 
You can export your yahoo calendar to a CSV file and import it into your google calendar. This method is somewhat manual and you will have to do this each time you create an event in your yahoo calendar. More details
Use Yahoo! app for android
You can use the official app for android developed by yahoo inc. to access your yahoo calendar as well as your mail, news, IM, videos and more. Download from the Play Store
Use third party apps to calendar syncing
There are many apps in tur play store which can be used to do this. CalcSync is an app which syncs yahoo caoendar with the stock calendar.