PHP - getting last statements PK ID to use in second function Insert statement

Duplicate Edit: This question is different because I'm trying to return a specific value, the primary key ID to be used in another functions INSERT statement as a foreign key, within the same action. The "duplicate" question does not answer this, rather it only shows how to get a return value from a function. Not how to get it and insert it correctly in another functions prepare statement. Which I wasn't sure I was doing correctly.

I have two tables, orders and customers that are to have data inserted from one form within the same action. The orders table has a primary key = orderID which also needs to be added into the customers table.

DB Relationship Diagram

I can upload the data to the orders table without a problem, but the second query function to the customers table does nothing. I'm pretty sure it's due to the foreign key constraint I've set. I've done some research and realize I need to get the foreign key id, possibly using $mysqli->insert_id or PDO::lastInsertId, but I'm lost as to how to use it with my current functions.

index.php

$product = $_POST['product'];
$fName = $_POST['fName'];
$lName = $_POST['lName'];
$address = $_POST['address'];
$address2 = $_POST['address2'];
$city = $_POST['city'];
$state = $_POST['state'];
$zip = $_POST['zip'];
$country = $_POST['country'];
$phoneNumber = $_POST['phoneNumber'];
$email = $_POST['email'];
/* Functions */
order_Data ($db, $product, $fName, $lName, $email);
// Need to have orderID  from ^ table used in order_custData sql statement
order_custData($db, $orderID, $fName, $lName, $address, $address2, $city, $state, $zip, $country, $phoneNumber, $email);

functions.php

<?php 

/**  Order Data Function
 */
function order_Data($db, $product, $fName, $lName, $email) {
    try {
        $sql = "INSERT INTO orders SET product = :product, fName = :fName, lName = :lName, email = :email";
        $ps = $db->prepare($sql);
        $ps->bindValue(':product', $product);
        $ps->bindValue(':fName', $fName);
        $ps->bindValue(':lName', $lName);
        $ps->bindValue(':email', $email);
        $ps->execute();
        return $orderID = $db->lastInsertId();
    } catch (PDOException $e) {
        die("Sorry, There was a problem order table.");
    }
}

/**  Customer Purchase Information Function
 * @param $orderID -- I need to insert the orderID from orders table?
 */
function order_custData($db, $orderID, $fName, $lName, $address, $address2, $city, $state, $zip, $country, $phoneNumber, $email) {
    try {
        $sql = "INSERT INTO customers SET  orderID = :orderID, fName = :fName, lName = :lName, address = :address, address2 = :address2,city = :city, state = :state, zip = :zip, country = :country, phoneNumber = :phoneNumber, email = :email";
        $ps = $db->prepare($sql);
        $ps->bindValue(':orderID', $orderID); // Foreign key from orders table
        $ps->bindValue(':fName', $fName);
        $ps->bindValue(':lName', $lName);
        $ps->bindValue(':address', $address);
        $ps->bindValue(':address2', $address2);
        $ps->bindValue(':city', $city);
        $ps->bindValue(':state', $state);
        $ps->bindValue(':zip', $zip);
        $ps->bindValue(':country', $country);
        $ps->bindValue(':phoneNumber', $phoneNumber);
        $ps->bindValue(':email', $email);
        return $ps->execute();
    } catch (PDOException $e) {
        die("Sorry, There was a problem with the customer table!");
    }
}
?>

Now the $orderID and :orderID IN THE order_custData function are just there for me as a visual representation to figure out the problem. I wasn't try to execute the sql statement with it originally. However, anything I've tried seems to throw errors underfined variable or fatal calls to the prepare function of the first function.

Thank you for your time.