<?php $tel1 = get_post_meta($post->ID, 'tel1', true);
if (!empty ( $tel1 )) {
<li ><?php the_field('tel1'); ?></li>
<?php } ?>
<?php $tel1 = get_post_meta($post->ID, 'tel1', true);
if (!empty ( $tel1 )) {
<li ><?php the_field('tel1'); ?></li>
<?php } ?>