with mask (id, mask, num) as (
  select 1, '999\-999\-99\-99', '4959009876' from dual
  union all
  select 2, '\+\7\(999\)999\-99\-99\;\1', '4959009876' from dual
  union all
  select 3, '\9\-\8\-9999999999\;', '4959009876' from dual
),
parse(id, mask, num, lvl, msk) as (
  select 
    id, mask, num, 1, regexp_replace(mask, '9{1}', substr(num, 1, 1), instr(replace(mask, '\9', '\x'), '9', 1, 1), 1) msk
  from mask m
  union all
  select 
    m.id, m.mask, m.num, p.lvl+1, regexp_replace(p.msk, '9{1}', substr(m.num, p.lvl+1, 1), instr(replace(m.mask, '\9', '\x'), '9', 1, p.lvl+1), 1) msk 
  from parse p
  join mask m on m.id = p.id and p.lvl+1 <= length(m.num)
)
select 
  mask, num, replace(msk, '\', '') as result
from parse
where lvl = length(num);

with m(id, mask, phone_num) as
(
  select 1, '999\-999\-99\-99', '4959009876' from dual
  union all
  select 2, '\+\7\(999\)999\-99\-99\;\1', '4959009876' from dual
  union all
  select 3, '\9\-\8\-9999999999\;', '4959009876' from dual
  union all
  select 4, '\9\-\8\-9999999999999\;', '4959009876123' from dual
  union all
  select 5, '\\\9\-\8\-9999999\;', '4959009' from dual
  union all
  select 6, 'Типа номер и всё такое: \9\-\8\-9999999\;', '4959009' from dual
  )
select 
    id, mask, phone_num, replace(replace(result, chr(254), '9'), chr(255), '\') as result
from m
model
    partition by (id)
    dimension by (0 dummy)
    measures (mask, replace(replace(replace(mask, '\9', chr(254)), '\\', chr(255)), '\') mask_filtered, phone_num, cast(null as varchar2(240)) result)
    rules iterate(1e9) until (substr(phone_num[0], iteration_number+2, 1) is null)
    (
        result[0] = regexp_replace(decode(iteration_number, 0, mask_filtered[0], result[0]), 
                                    '9', 
                                    substr(phone_num[0], iteration_number+1, 1), 
                                    instr(mask_filtered[0], '9', 1, iteration_number+1), 
                                    1
                                    )
    )
order by id;    


        ID MASK                                                        PHONE_NUM     RESULT                                                                                                                                                                                                                                          
---------- ----------------------------------------------------------- ------------- ------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
         1 999\-999\-99\-99                                            4959009876    495-900-98-76                                                                                                                                                                                                                                   
         2 \+\7\(999\)999\-99\-99\;\1                                  4959009876    +7(495)900-98-76;1                                                                                                                                                                                                                              
         3 \9\-\8\-9999999999\;                                        4959009876    9-8-4959009876;                                                                                                                                                                                                                                 
         4 \9\-\8\-9999999999999\;                                     4959009876123 9-8-4959009876123;                                                                                                                                                                                                                              
         5 \\\9\-\8\-9999999\;                                         4959009       \9-8-4959009;                                                                                                                                                                                                                                   
         6 Типа номер и всё такое: \9\-\8\-9999999\;                   4959009       Типа номер и всё такое: 9-8-4959009;