joining the where clause to select statement of two different tables
I'm not too sure what you are doing there and that's not at all how I write queries. Either way, I would try it this way:

select 
    a.MBR_ID_TYP_ID || '-' || b.ref_desc as "Member Type" , 
    a.*
from mbr_id as a
    left outer join ref as b 
    on  b.ref_nm = 'memberIDType' 
    and a.REF_CD = b.MBR_ID_TYP_ID    -- or: b.REF_CD = a.MBR_ID_TYP_ID 
                                      -- not clear from the code
where 
    a.mbr_id = 6484532;


I don't join in where clauses because that is really hard to read. 
I generally put the columns in the select portion, then do the joins in the from section. The filtering goes on in the where clause. Finally if necessary the order by is last, if I need to sort.