You are passing the parameters wrong, try with something like this:
function get_telephone($attrs) {
$attr = shortcode_atts( array(
'name' => 'John Doe'
), $attrs );
return attr['name'];
}
add_shortcode( 'telephone', 'get_telephone' );
In the post you call the shortcode like this: [telephone name="Jose"]
Anyway, inside the get_telephone
function you should add some logic to get the phone numbers from somewhere, it could be an array, or you could create a custom post type to store the numbers.