SQL Script to find Contract Numner from Oracle Purchasing (11.5.10.2)

I have the following script and can get contract_id but cannot get contract number. The contract number is blank but I cant get the contract_id. How can I change my script to get the contract_num.? Is there a join or another table.? Any help would be appreciated.

Thanks

SELECT ph.segment1 "PO_NUM",

  authorization_status,

  pov.segment1 as supplier_num,

  pov.vendor_name as vendor,

  pl.line_num "LINE_NUM",

  pl.po_line_id, 

  pl.po_header_id,

  pl.line_type_id, 

  pltb.order_type_lookup_code, 

  pl.item_id, 

  pl.item_description, 

  pl.unit_price,

  pl