jibatma ji,

It's not that a Phd student need not worry about the H1-B cap at all as it depends on which type of organization you plan to join.

The regulation says that H1-B workers, if employed at a university, affiliated non-profit entity, non-profit research organizations or government research organizations are not subject to annual H1B cap.

So, Phd students or for that matter ANYONE who plans to join any of the above mentioned organizations, need not worry about the H1-B cap and can file the petition anytime. Thanks.