get parent category only

by

Try this:

$post = get_post(); // If $post is already available, skip.
$terms = get_the_terms( $post->ID, 'category' );
foreach ( $terms as $term ) :
    if ( $term->parent === 0 ) :
        echo '<a href="' . esc_url( get_term_link( $term->term_id, 'category' ) ) . 
            '" title="' . esc_html( $term->name ) . '" ' . '>' . esc_html( $term->name ) . 
            '</a> ';
    endif;
endforeach;