/*
 * Add columns to podcasts list
 */
 function add_acf_columns ( $columns ) {
   return array_merge ( $columns, array ( 
     'episode_number' => __ ( 'Episode Number' ),
   ) );
 }
 add_filter ( 'manage_podcast_posts_columns', 'add_acf_columns' );

/*
 * Add columns to podcasts list
 */
 function podcast_custom_column ( $column, $post_id ) {
   switch ( $column ) {
     case 'episode_number':
       echo get_post_meta ( $post_id, 'episode_number', true );
       break;
   }
 }
 add_action ( 'manage_podcast_posts_custom_column', 'podcast_custom_column', 10, 2 );

function episode_number_column_register_sortable( $columns ) {
	$columns['episode_number'] = 'episode_number';
	return $columns;
}
add_filter('manage_edit-podcast_sortable_columns', 'episode_number_column_register_sortable' );