Who wrote your schema, MC.Escher????

The "AND owner_id IN" might work better with a temporary table. You also mave way too many LIKE AND BETWEEN clauses. That this query even runs is a testament to the power of a modern database. My sugestion, total rewrite of the schema.

Code:
SELECT DISTINCT ph.k_po_num, 
                pd.supp_id                                 supp_id, 
                ph.po_status_flg                           po_status_flg,
                cs_udf.cs_getdatefromjulian(ph.created_dt) created_dt,
                ph.source_doc_type
  FROM 
     ( SELECT k_po_num, k_comp_id, po_status_flg, created_dt, source_doc_type
         FROM po_headers
        WHERE k_comp_id   = :263
          AND active_flg  = 'A'
          AND k_po_num         LIKE :264
          AND ph.created_by    LIKE :267
          AND ph.po_stage_flg  LIKE :272
          AND ph.po_status_flg LIKE :273
          AND ph.created_dt    BETWEEN 
              cs_udf.cs_nvln(cs_udf.cs_setdateinjulian(
                             cs_udf.cs_to_date(:274, 'YYYYMMDD')), 
              ph.created_dt)
          AND cs_udf.cs_nvln(cs_udf.cs_setdateinjulian(
                             cs_udf.cs_to_date(:275, 'YYYYMMDD')), 
                             ph.created_dt )
          AND ph.close_dt      BETWEEN 
              cs_udf.cs_nvln(cs_udf.cs_setdateinjulian(
                             cs_udf.cs_to_date(:276, 'YYYYMMDD')), 
              ph.close_dt) 
          AND cs_udf.cs_nvln(cs_udf.cs_setdateinjulian(
                             cs_udf.cs_to_date(:277, 'YYYYMMDD')), 
              ph.close_dt)
     ) ph
 INNER JOIN 
     ( SELECT
         FROM po_details
        WHERE pd.active_flg IN ('A', 'I')
          AND ph.owner_id  <> :262
          AND pd.supp_id LIKE :261
          AND pd.item_id BETWEEN 
              cs_udf.cs_nvlc(:265, pd.item_id) 
          AND cs_udf.cs_nvlc(:266, pd.item_id)
     ) pd
    ON ph.k_po_num  = pd.k_po_num
   AND ph.k_comp_id = pd.k_comp_id
   AND pd.dc_id  BETWEEN 
       cs_udf.cs_nvlc(:268, pd.dc_id) 
   AND cs_udf.cs_nvlc(:269, pd.dc_id)
   AND pd.eta_dt BETWEEN 
       cs_udf.cs_nvln(cs_udf.cs_setdateinjulian(
       cs_udf.cs_to_date(:270, 'YYYYMMDD')), pd.eta_dt) 
   AND cs_udf.cs_nvln(cs_udf.cs_setdateinjulian(
       cs_udf.cs_to_date(:271,'YYYYMMDD')),  pd.eta_dt)
 INNER JOIN
     ( SELECT 
         FROM item_dcs 
        WHERE active_flg = 'A'
          AND owner_id IN 
            ( :1,  :2,  :3,  :4,  :5,  :6,  :7,  :8,  :9, :10, 
             :11, :12, :13, :14, :15, :16, :17, :18, :19, :20,
             :21, :22, :23, :24, :25, :26, :27, :28, :29, :30,
             :31, :32, :33, :34, :35, :36, :37, :38, :39, :40,
             :41, :42, :43, :44, :45, :46, :47, :48, :49, :50,
             :51, :52, :53, :54, :55, :56, :57, :58, :59, :60,
             :61, :62, :63, :64, :65, :66, :67, :68, :69, :70,
             :71, :72, :73, :74, :75, :76, :77, :78, :79, :80,
             :81, :82, :83, :84, :85, :86, :87, :88, :89, :90,
             :91, :92, :93, :94, :95, :96, :97, :98, :99, :100,
             :101, :102, :103, :104, :105, :106, :107, :108, :109, :110,
             :111, :112, :113, :114, :115, :116, :117, :118, :119, :120,
             :121, :122, :123, :124, :125, :126, :127, :128, :129, :130,
             :131, :132, :133, :134, :135, :136, :137, :138, :139, :140,
             :141, :142, :143, :144, :145, :146, :147, :148, :149, :150,
             :151, :152, :153, :154, :155, :156, :157, :158, :159, :160,
             :161, :162, :163, :164, :165, :166, :167, :168, :169, :170,
             :171, :172, :173, :174, :175, :176, :177, :178, :179, :180,
             :181, :182, :183, :184, :185, :186, :187, :188, :189, :190,
             :191, :192, :193, :194, :195, :196, :197, :198, :199, :200,
             :201, :202, :203, :204, :205, :206, :207, :208, :209, :210,
             :211, :212, :213, :214, :215, :216, :217, :218, :219, :220,
             :221, :222, :223, :224, :225, :226, :227, :228, :229, :230,
             :231, :232, :233, :234, :235, :236, :237, :238, :239, :240,
             :241, :242, :243, :244, :245, :246, :247, :248, :249, :250,
             :251, :252, :253, :254, :255, :256, :257, :258, :259, :260)
        ) id
    ON pd.dc_id     = id.k_dc_id
   AND pd.k_comp_id = id.k_comp_id
   AND cs_udf.cs_trim(pd.item_id) = cs_udf.cs_trim(id.k_item_id);