The Current State of Telephone Links | CSS-Tricks

The linked article Show archive.org snapshot shows what current browsers do when you click a link like this:

Copy<a href="tel:1-562-867-5309">1-562-867-5309</a>

Spoiler: The current state is sad

It's still the case that most desktop browsers can't do something useful with tel: links. They will usually open a dialog confirming that an external application will be opened. If the user confirms, she will see an error, or nothing at all.

On mobile browsers on the other hand, these links just open the internal phone app, which is very useful.

Unfortunately you cannot detect whether a browser will do something useful with a tel: link. Your best options seem to be:

1. Don't have tel: links and rely on the mobile browsers to automatically link phone numbers (which some do)
2. Do have tel: links, but only style them (with color, underline) on small screens.