WP_query hooks before execute a search query

To avoid the splitting of searchphrases, use the sentence query variable in the pre_get_posts hook:

function only_search_for_full_phrase( $query ) {
    if ( $query->is_search() && $query->is_main_query() ) {
        $query->set( 'sentence', true );
    }
}
add_action( 'pre_get_posts', 'only_search_for_full_phrase' );

Didn’t test it, but should do the trick.

Happy Coding!