If you have uploaded a portrait photo and we have approved it, it is visible to all users at all times. It is not possible to make the portrait photo temporarily invisible like the photos in your photo gallery (see also: Can I make my individual photos in my photo gallery invisible to other users?). The only option is to delete the portrait photo from your profile entirely. If you later wish to display a portrait photo, you would have to upload a new one (see also: How do I upload a new portrait photo or change/delete an existing one?).