$page_info="";

for($i=1; $i<=$totalpage; $i++){

    $productResource = $shopify->Product();

    $params = array(

                'limit' => '250',

                'page_info' => $page_info

              );

    $product = $productResource->get($params);

    $nextPageProducts = $productResource->getNextPageParams();

    $page_info = $nextPageProducts['page_info'];

}