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.