Why is the phone number a hyperlink on desktop sites, in my widget?

I think I see the problem now. None of your links have a closing anchor tag which is cascading down until it hits the end at which point you close it on phone number:

Your Code:

echo  '<a href="'.$facebook.'" target="_blank"><img src="'. get_stylesheet_directory_uri() .'/images/fb.png" height="24" width="24" alt="facebook">';

What it should probably look like:

echo  '<a href="'.$facebook.'" target="_blank"><img src="'. get_stylesheet_directory_uri() .'/images/fb.png" height="24" width="24" alt="facebook"></a>';

So after you link your images in your callback function you need to close your anchor tags.