1. Store every page form info in user session. you can do this by using $_SESSION PHP variable. But note that you must call session_start before using this.
$_SESSION["PAGE1"] = array (
'var1' => 'value1',
'var2' => 'value3',
....
);
2. You can put a hidden input in every page for and serialize data collectedfrom other pages into this hidden input. you can optionally choose base64_decode/base64_encode and json_encode/json_decode to serialize your data or you can use PHP builtin serialize/unserialize functions.
$serializedData = base64_encode ( json_encode ( $_POST ) );
$originalData = json_decode ( base64_decode ( $serializedData ) );
Hope it helps