Primary Category Yoast 1

$category_index = 0;
foreach( $post->post_categories as $category ) {
    $category_index++;
    $separator =  $category_index < count(  $post->post_categories ) ? ', ' : '';
    echo '<a href="'. esc_url( $category['permalink'] ) .'" title="' . esc_attr( $category['label'] ) . '">' . esc_html( $category['label'] ) . '</a>' . $separator;
}