You can add custom phone number validation by adding the code below in your theme functions.php file

add_filter( "adverts_form_load", function( $form ) {
    if( $form["name"] != "advert" ) {
        return $form;
    } 
    foreach( $form["field"] as $k => $f ) {
        if( $f["name"] == "adverts_phone" ) {
            $form["field"][$k]["validator"][] = array( "name" => "my_is_phone_number");
        }
    }
    return $form;
});
function my_is_phone_number( $data ) {
    if(preg_match("/^[0-9]{3}-[0-9]{3}-[0-9]{4}$/", $data)) {
        return true;
    } else {
        return "invalid";
    }
}

In the preg_match() function you just need to update the patter to allow the phones in your desired format.