John,
This is a delayed reply but thank you for your answer. I was stuck with the mindset of only outputting this to an HTML page for view and totally missed using this great feature provided by ACF. Thank you again.
Elliot answered a similar question here. In order to call a field while on index.php, you need to add the page_ID like this: <?php the_field('page_intro_text', 15); ?>
where the number ’15’ is the value of page_ID for the page that has the field 'page_intro_text'
.