Sort on two variables

So long as every listing has a feature_posi field (even if it’s empty), you can let WordPress/MySQL handle the ordering for you:

$args = array(
    'post_type'      => 'listing',
    'posts_per_page' => -1,
    'orderby'        => 'title meta_value_num',
    'order'          => 'ASC',
    'meta_key'       => 'feature_posi',
    'tax_query'      => array(
        array(
            'taxonomy' => $taxonomyName,
            'field'    => $term_slug,
            'terms'    => get_queried_object()->term_id,
        )
    )
);