Bookmarks link's creator first name and phone details

PREFIX sioc: <http://rdfs.org/sioc/ns#>
PREFIX sioct: <http://rdfs.org/sioc/types#>
PREFIX foaf: <http://xmlns.com/foaf/0.1/>
CONSTRUCT
  {
    ?post foaf:maker ?maker .
    ?maker foaf:firstName ?fname .
    ?maker foaf:phone ?phone .
  }
WHERE 
  {
    ?forum a sioct:BookmarkFolder .
    ?forum sioc:container_of ?post.
    optional{ ?post foaf:maker ?maker }.
    optional{ ?maker foaf:firstName ?fname  } .
    optional{ ?maker foaf:phone ?phone } .
  }