incoming yahoo email is encrypted on desktop. Fine on i pphone

In TB open Settings from the 3 bar icon.  In the General Section you'll see the option for setting it as the default email client.

As far as Contacts, open that section in Yahoo and in the 3 dot menu you'll see an option to Export to CSV file.  Once you have that file, open the Address Book in TB and you'll see an import option.

Just a wild stab, but are you using Windows Mail?  I ask because it's broken when it comes to Yahoo-based email accounts and you'll get emails that display with a bunch of gibberish.  It's not really encrypted, just some of the raw data that you don't normally see.

To fix it change to a different email client.  I recommend Thunderbird since it supports OAuth2 that's required by Yahoo but there are others like BlueMail and eM Client that people seem to like.

Thanks for your response.  I was able to download Thunderbird.  I can open up email and read entirety but can't figure out how to make it my default email or how to transfer my contacts.  This may be way over my head.