SQL & PL/SQL

I would like to store all phone numbers as 1112223333.
How can I strip out all other characters (ex. ()-) prior to inserting in table?

I created the following however, if someone insertst a space (ex. (212) 555-1212) it does not work:

declare
v_phone varchar2(35);
begin
v_phone := '(212)555-1212';

for i in 1..length(v_phone) loop
if substr(v_phone,i,1) not in ('0','1','2','3','4','5','6','7','8','9') then
select replace(v_phone,substr(v_phone,i,1),'') into v_phone from dual;
end if;
end loop;
dbms_output.put_line(v_phone);
end;