How to include a JSON file on my page?

You can do this with PHP indeed. The steps are as followed;

1. Get the contents of the JSON file within a variable using $json = file_get_contents('path-to-file.json')
2. Inside your <script> tags parse the JSON contents within a Javascript variable like this; var jsonContent="<?= $json; ?>";
3. Debug the contents in your Javascript environment using the following; console.log(JSON.parse(jsonContent));