About CategoryList() – what parameters should be given to display parent childs

Hello,
I’m struggling to find a way to had the below code (used in the form in the homepage search)

echo $CORE->CategoryList(array($selcat1,”,0,THEME_TAXONOMY)); ?>

How should I change the above to show only certain parent ID child(s).
E.g my top category ID = 584. Now I would like to have only its child ID:585 and its children included to list output and that are then options in the selection input field.

For clarity my Categories structure is like below:
Phones (ID:584)
Apple (ID:585)
iPhone
Nokia
Lumia
Computers
Dell
Tablets
Samsung

Thanks in advance,
Ari from Finland