How to reduce repetitive code

You can define your own custom functions in PHP just like you would in JavaScript. Here’s your code example rewritten using a function:

$page = get_page_by_title('Excerpts Showreel'); <-- This piece of code will change

// the code below will never change.
function get_my_content( $page ) {
    $my_id = $page;
    $post_id = get_post($my_id, ARRAY_A);
    $title = $post_id['post_title'];
    $content = $post_id['post_content'];

    return $content;

echo get_my_content($page);

So long as you have your get_my_content() function defined, you can use it anywhere you need to.