How to add text & call to action button to featured image on homepage?

If your theme allow you to edit the text displayed on your home page, when you just need to add a a link.

A click to call link is a simple HTML link, except that the value of the href attribute needs to refer to the “tel” protocol:

<a href="https://wordpress.stackexchange.com/questions/278772/tel:XXXXXXXXXXXXX">Call Us</a>

Where “XXXXXXXXXXXXX” is your phone number.

If you only use the graphic interface, simply write “Call Us”, highlight it and click on the button to add a link, and put “tel:XXXXXXXXXX” as the url.