Adding html and phone number button to tagline?

How can I add the following html to my header’s tagline?

<a href="000-000-0000">(000)000-0000</a>

I’m using a child version of the theme, but I didn’t see an obvious way to do this in the header.php file (but I don’t speak php either.).

I want to allow mobile phone users to see that they can click-to-call, the second that they land on the site.