How to pass ID of the post in modal window in php code?

Good.

When you click on a post opens a modal window.

Code in a modal window.

<?php$id = 70;echo do_shortcode( ''.get_field('slider_exercises', $id).'' );?>

Code prints gallery from post using the ACF plugin. If you do not specify the $id of the post, and the gallery will not display.
JS when clicking on a post takes the post id and places any specified attribute modal window.
How to put this id into a variable $id in php code, or how to pull out the php code id attribute from html.
Or maybe there is another way?

Thank you!