In your comment you mentioned that you had a reviews post type. This means that /reviews/ will be the default URL for listing that post type, and this will use index.php as per the template hierarchy. If you’re trying to list reviews, then my first suggestion would be to just use the post type archive, and create archive-reviews.php to markup and style them.
If you do ultimately need a static page that list reviews, rather than the post type archive, then set the has_archive property of the post type to false. Then /reviews/ won’t exist anymore, and you can use it as the slug for a new page instead.