How do I make my single-work page show on my front-page.php?

No CODE is necessary for this.

Go to WordPress Admin Panel → Settings → Reading.

Then from the option Your homepage displays, select A static page (select below) & then in the Homepage: dropdown menu, select your Work page & Save Changes.

Like the screenshot below:

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Of course, once you’ve done this, your Work page content will be loaded on the site home page (e.g. www.example.com) with proper home page template (e.g. front-page.php) of your theme.

Check the Template Hierarchy document to learn which theme template will handle the home page in different situations.

Custom Home Page Template

Say you have a template file (within the theme) named single-work.php and another template file front-page.php. According to WordPress template hierarchy, front-page.php will load the home page, regardless of the setting Your latest posts or A static Page.

You can change that if you choose A static page. Let’s say you have a static page named Work & you select this page as your Homepage. Now, first, put the following CODE at the top of single-work.php template file:

<?php
    /* Template Name: Work Template */

Then edit work page and you’ll see the Template selection option under Page Attributes:

From there, select Work Template and save. That way, the home page will load using single-work.php template instead of front-page.php.

Note: if you don’t see the Page Attributes meta box, then select Page Attributes from top right Screen Options drop down menu.