Email signature social media icon won't show

Email signature social media icon won't show

I inserted a facebook icon and an instagram icon into my email signature.  I highlighted both icons to embed links in them.  I did many email tests and also redo the works many times, but the two icons won't show up when you open up the email using the iphone default email app.  There were just two white boxes.  If you click on those white boxes then the links would work though.  However, if you use a laptop to check the email, then the icons and links showed up and worked fine.  It was just looking at the email through the iphone default email app that was having the problem.  Thanks.