How to select stored procedure output parameters as a table in oracle sql developer

I have a procedure

create or replace PROCEDURE proc
(
  p1 IN varchar2,
  p2 IN varchar2,
  p3 OUT varchar2
) AS
BEGIN
 p3:= p1 || ' ' || p2
END proc

I call it by

Declare
  P3 varchar(50);
Begin
 proc('foo', 'bar', P3)
END;

I can print out the value of P3 using

Dbms_Output.Put_line('P3: ' || P3)

But I need to get the result as a table I can select from. Best way I can think of is

Declare
  P3 varchar(50);
Begin
 proc('foo', 'bar', P3)
END;
SELECT &&P3 from dual;

But that gives me an error

Error report -
ORA-06550: line 5, column 12:
PL/SQL: ORA-00936: missing expression
ORA-06550: line 5, column 5:
PL/SQL: SQL statement ignored
06550. 00000 - "line %s, column %s:\n%s"
*Cause: Usually a PL/SQL compilatiopn error.
*Action:

Is there some way of selecting the value of a parameter as a column/row value?

I need this all done inside the single sql query because I need to executed it from another server via linked server.

I don't have permission to create any other stored procedures, functions or tables on the database.

To me, the most straightforward option is to create a function - it is supposed to return a value:

create or replace function proc (p1 IN varchar2, p2 IN varchar2)
  return varchar2
AS
BEGIN
  return p1 || ' ' || p2;
END proc;

Then you'd call it as e.g.

select proc('a', 'b') from dual;

Saying that you "don't have permission to create ... functions" - well, if you are granted to create a PROCEDURE, then you are also granted to create a FUNCTION. It is the same privilege.

If you can only use procedures that are already created, then:

SQL> create or replace PROCEDURE proc
  2  (
  3    p1 IN varchar2,
  4    p2 IN varchar2,
  5    p3 OUT varchar2
  6  ) AS
  7  BEGIN
  8    p3:= p1 || ' ' || p2;
  9  END ;
 10  /

Procedure created.

SQL> var result varchar2(20)
SQL>
SQL> exec proc('a', 'b', :result);

PL/SQL procedure successfully completed.

SQL> print :result

RESULT
--------------------------------
a b
    
SQL> select :result from dual;

:RESULT
--------------------------------
a b

SQL>