display list of attached images of a page or post excluding featured image

wpattachedsamples.php

<?php
//get featured image ID
$thumb_ID = get_post_thumbnail_id( $post->ID );

//attachement loop - with exclude argument for featured image
$args = array(
'orderby' => 'menu_order',
'post_type' => 'attachment',
'post_parent' => get_the_ID(),
'post_mime_type' => 'image',
'post_status' => null,
'posts_per_page' => -1,
'exclude' => $thumb_ID
);
$attachments = get_posts($args);
?>

<?php
//Goes inside loop
function getAttachedImagesButThumbnail() {
$post_thumbnail_id = get_post_thumbnail_id( $post_id );
$images =& get_children( 'post_type=attachment&post_mime_type=image&post_parent=' . $post->ID );
foreach( $images as $imageID => $image ) {
    if ( $image->ID == $post_thumbnail_id) {
        unset ($images[$imageID]);
    } else {
        $out .= wp_get_attachment_image($imageID, array(285,285), false);
    }
}
return $out;
}
?>

<?php if ( $post->post_type == 'data-design' && $post->post_status == 'publish' ) {

        $attachments = get_posts( array(
            'post_type' => 'attachment',
            'posts_per_page' => -1,
            'post_parent' => $post->ID,
            'exclude'     => get_post_thumbnail_id()
        ) );
 
        if ( $attachments ) {
            foreach ( $attachments as $attachment ) {
                $class = "post-attachment mime-" . sanitize_title( $attachment->post_mime_type );
                $thumbimg = wp_get_attachment_link( $attachment->ID, 'thumbnail-size', true );
                echo '<li class="' . $class . ' data-design-thumbnail">' . $thumbimg . '</li>';
            }
             
        }
    }
?>

<?php
	$thumb_ID = get_post_thumbnail_id( $post->ID );
	echo $thumb_ID;
	$gall = '[gallery exclude="'.$thumb_ID.'"]';
	echo $gall;
	echo do_shortcode($gall);
?>