I don't have 9i to test with right now, but I'll hazard a guess:
Select distinct N_PHN_AREACD
left outer join
( select N_PHN_INSTID, N_PHN_AREACD
where N_PHN_PHTYP = 'D'
and N_PHN_PHTYP = 'E'
on COUNT_INSTID = N_PHN_INSTID;
BTW it would help us to help you if you used table aliases so we don't have to guess what columns come from what tables, and if you were consistent about use of upper/lower case throughout your query to aid readability ;-)