How do I show a summary of the fields filled out?

I agree with Lewis that to give a better answer would require seeing the code involved, but to at least address the question about the lifetime of variables, in addition to what Lewis said about local scope, it should be noted that variables will not carry over with a new page request, even if it's the same page. This is because HTTP and PHP are stateless, meaning each request (new page or page reload) remembers nothing from the one before it. Any such abstraction (such as sessions) only mimics the behavior of remembering state, but each HTTP request is distinct and any data that needs to get passed around, needs to be passed on each request.

You should be able to accomplish this through the use of sessions, databases, files, or passing the variables back through either a GET or POST request.

Without being able to see everything this is abit hard however if you are trying to declare a varible on the thankyoupage you need to one make sure that the varible is not just sotred in a function because if it is then outside of the function it will not work.

Secondly you need to determine whether you have ended your php loop for example because if so it will end that script running and therefore you wont be able to declare the variable.

If this does not make sense feel free to message me further.

Thanks Lewis and Benjamin. The variable is in an if statement but not a function. I've tried initialising the variable outside the if statement but that didn't work. Here's the original code:

<?php

// If we set method=post in the form
if($_SERVER["REQUEST_METHOD"] == "POST") {
  // we take the values from the fields from the suggestion form using post method
  $name = $_POST['name'];
  $email = $_POST['email'];
  $detail = $_POST['details'];

  // create a variable to hold all the values from the form
  $email_body = '';
  $email_body .= "<div>Name: {$name}</div>";
  $email_body .= "<div>Email: {$email}</div>";
  $email_body .= "<div>Details: {$detail}</div>";

  // redirect to the thank you page
  header("location:suggest.php?status=thanks");
}

?>

And the part where I'm trying to output the $email_body variable:

    <?php
      if(isset($_GET['status']) && $_GET['status'] == 'thanks') { ?>
        <div class="wrapper">
        <h1>Thank you<h1>
        <p>Thanks for the email. I'll check out your suggestion</p>
        //Trying to call it HERE
        <p><?php echo $email_body; ?></p>
        </div>
     <?php } else { ?>

Note: the form is located on the suggest.php page and the thank you is same page with ?status=thanks