Query posts alphabetically within this function

You’ll need to run through get_posts() to apply the order by handling.

$planIDs = get_post_meta( $post->ID, '_lm_comm_plans', false );
foreach( get_posts( array( 'post__in' => $planIDs, 'orderby' => 'name', 'order' => 'ASC', 'post_type' => 'plans' ) ) as $plan ) {
    $pdfID = get_post_meta( $planID, '_lm_plan_pdf', true );
    $pdfURL = wp_get_attachment_url( $pdfID );
    $planTitle = get_the_title( $planID );
    ?>
    <li class="plan"><!-- content here --></li>
    <?php
}