Phone number validation in varchar2 field

:phone_number := :code||'-'||:ph_no

99999-99999

CREATE OR REPLACE FUNCTION strip_bad (p_string IN VARCHAR2) 
RETURN VARCHAR2 
IS 
good_string VARCHAR2(63) := '1234567890 ' || '-' ||  ; 

BEGIN 

RETURN 

TRANSLATE (p_string, 'T' || 
TRANSLATE ( p_string, '.' || good_string 
, '.' 
) -- find the bad characters 
, 'T'); -- remove the bad characters 
END strip_bad; 
/ 

-- For Example :

select strip_bad('St. Loui$$s') NOW_BAD from dual 
/ 

NOW_BAD 

SELECT CASE WHEN REGEXP_LIKE('23444-34545','^[0-9]{5}-[0-9]{5}$') 

THEN 'Match Found' else 'No Match Found' end as output from dual;

DECLARE
    v_num NUMBER;
BEGIN
    v_num := TO_NUMBER(:YOUR_BLOCK.YOUR_ITEM); -- assuming it's a char field
EXCEPTION
    WHEN OTHERS THEN
        MESSAGE('Please enter in Format 99999');
        RAISE FORM_TRIGGER_FAILURE;
END;

If the user try to insert zero in the code in starting position then it does not allowed by CODE. it automatically