$data = [1,2,3,4,5,6,7,8,9];
$perPage = 2;
$page = $_GET['page'] ?? 1;
$count = $page * $perPage;
$display = array_slice($data, 0, $count);
foreach ($display as $item) {
echo '<div>'.$item.'</div>';
}
echo '<a href="index.php?page='.($page+1).'">Показать ещё</a>';