Problems with Sub Query

Question

Hello, I am attempting to create a sub query to display certain information. On the form that the information is inputted, the user has the option of inputting a phone number extension if applicable. If this is the case I want the phone number to show as 555-867-5309 (x1234). However without the problem checks, the (x ) will show up regardless and looks sloppy. Here is the code I have, please advise.
There will be two spots this will be needed -- for the requester's contact number and the app manager (sme) contact information.
Thanks.
select
    pm.pk_proj_master_id "Project Number",
    pm.trackit_work_order "TrackIt Work Order",
    pm.name "Project Name",
    pm.status "Project Status",
    req.last_name||', '||req.first_name||', '||req.middle_initial||'.' "Requestor Name",
    rde.department_group_descr "Requestor Department Name",
    req.department_descr "Requestor Division Name",
    pm.requester_ext,
    case
        when pm.requester_ext in
            select
                pm.requester_phone|| '(x'||pm.requester_ext ||')' "Requesters Number"
            from
                protrac_master pm
            where
                pm.requester_ext is not null
        else
            select
                pm.requester_phone "Requesters Number"
            from
                protrac_master pm
    end as "Requester Number",
    man.last_name||', '||man.first_name||', '||man.middle_initial||'.' "SME Name",
    mdg.department_group_descr "SME Department Name",
    man.department_descr "SME Division Name",
    pm.app_manager_ext,
    case
        when pm.app_manager_ext in
            select
                pm.app_manager_phone|| '(x'||pm.app_manager_ext ||')' "SME Number"
            from
                protrac_master pm
            where
                pm.app_manager_phone is not null
        else
            select
                pm.app_manager_phone "SME Number"
            from
                protrac_master pm
    end as "Requester Number",
    pm.createby_date "Date Entered",
    pm.date_begin "Date Began",
    pm.date_completed "Date Completed",
    pm.estimated_date "Estimated Completion Date"
from
    protrac_master pm,
    cobr.vw_pps_payroll req, cobr.department_group rde,
    cobr.vw_pps_payroll man, cobr.department_group mdg
where
    pm.requester_id         = req.emple_no and
    pm.requester_dept_id    = rde.pk_department_group_id and
    pm.app_manager_id       = man.emple_no and
    pm.app_manager_dept_id  = mdg.pk_department_group_id
order by
    pm.pk_proj_master_id

Answer 1

I think you can avoid the whole sub query thing just by using the NVL2 function:
select ...
     , NVL2( pm.requester_ext
           , pm.requester_phone|| '(x'||pm.requester_ext ||')'
           , pm.requester_phone) "Requesters Number"
     , NVL2( pm.app_manager_ext
           , pm.app_manager_phone|| '(x'||pm.app_manager_ext ||')'
           , pm.app_manager_phone) "Manager Number"
  from protrac_master pm
     , ...