what rating is the movie "HP order of the pheonix"

I'm not sure how the ratings work in other countries, but here in the US, it's PG13 -- which means it may be inappropriate for children under the age of thirteen.

It is PG 13. PG 13 doesn't necessarily mean exactly the age of thirteen.
Though, it is strongly suggested that the parent check if the movie is appropriate for their child 또는 not. Some of the material may be inappropriate, if 당신 are not of the right age.
But that is not always the case.
Harry Potter is an exception, for there is no nudity, swearing, drugs etc in the OoTP. Even so, 당신 should have a parent check if 당신 can watch 또는 not. Hope that helped! :)