How to use dashicons
You insert dashicons anywhere on the page but you first need to import them.
Add the following PHP code to your functions.php or inside a functionality like Code Snippets:
add_action( 'wp_enqueue_scripts', 'load_dashicons_front_end' );
function load_dashicons_front_end() {
wp_enqueue_style( 'dashicons' );
}
Now, you can visit the dashicons website, copy the HTML code and paste it anywhere you want. As an example, you could paste the code inside the Navigation Label of a menu item on the admin.
You might need to add additional CSS to line up the icon with the rest of the content.
.menu .dashicons-phone {
margin-top: 18px;
margin-right: 8px;
}