I was able to fix it!
I changed my code to:
<?php $args = array( 'posts_per_page' => -1, 'post_type' => 'siteinfo' );
$myposts = get_posts( $args );
foreach ( $myposts as $post ) : setup_postdata( $post );
$phone = get_field('phone_number'); ?>
<div class="phone">
<p><img class="phone-img" src="<?php bloginfo('template_directory'); ?>/images/phone.png" alt="<?php bloginfo('name'); ?>" /><span><?php echo $phone; ?></span></p>
</div><!--end.phone-->
<?php endforeach;
wp_reset_postdata();?>
Thanks for your help!