You can find lots of information about how to create HTML links to call a phone number. The syntax is essentially
<a href="tel:NUMBER">NUMBER</a>. Most examples however would not work for people with disabilities.
Screen reader users often navigate links out of context, that is, go from link to link, skipping the text in between, so if you simply write
<a href="tel:555-2106">555-2106</a>, the screen reader will simply hear
555-2106, and that won't make much sense. To make a telephone link accessible, you need to add context information. One way to do this is to write the link in a phrase, for example
<a href="tel:NUMBER">call Example Organization at NUMBER</a>. When a screen reader user navigates to your link, they will hear
call Example Organization at NUMBER, and your link will make much more sense.