The hope was that ACF had something built in for bookmarks. Modifying templates requires more advanced knowledge and adds the risk of breaking other things, plus a template update (for non-custom themes) would lose the changes. The suggestion made by John only accounts for one section of the page, not multiple sections as a result of flexible content. – Thank you for the input, though.
I ended up creating a text field in my flexible content, so that I could define what would be used for the bookmark for each person’s content. I then modified the template to pull the text field’s content and apply it to the flexible content loop ID property. Fortunately our theme and templates are custom, so I don’t have to worry about losing changes in an update.
<?php
$staffname = get_sub_field('name');
$staffbiog = get_sub_field('bio');
$staffmark = '"' . get_sub_field('bookmark') . '"';
?>
<section class="block flex_detail" id=<?php echo $staffmark; ?>>
<article class="flexcon">
<div class="flexentry">
<header>
<h4><?php echo $staffname; ?></h4>
</header>
<?php echo $staffbiog; ?>
</div>
</article>
</section>
