as far as phasing goes you'd need to make custom GANIs, nick, and chat system to get something like that working.
Other option is to have the base levels stored somewhere and make new copies with some sort of suffix to the level name ("baselevel_leaderaccount" maybe) and send players to the new copies of levels individually.
The second option is probably superior to the first as NPC interaction for the first would be a pain to manage.
PHP Code:
function newInstance( pobj)
{
copylevel("baselevel", "instances/baselevel_" @ pobj.account);
}
not on RC or I'd test if you need a file type at the end.