REGEXP_COUNT(phones,',') + 1

LENGTH(phones) - LENGTH(REPLACE(phones,',')) + 1

with t as (
           select  phones,
                   regexp_count(phones,',') + 1 phone_count,
                   case regexp_count(phones,'\[')
                     when 0 then '()'
                     else '(0' || regexp_replace(phones,'(^|\])[^[]*(\[|$)','+') || '0) div ' || regexp_count(phones,'\[')
                   end avg_expr
             from  phone
          )
select  phones,
        phone_count,
        xmlcast(
                xmlquery(
                         avg_expr
                         returning content
                        )
                as number
               ) average
  from  t
/

PHONES                                             PHONE_COUNT    AVERAGE
-------------------------------------------------- ----------- ----------
89111111111[2], 89112222222[3]                               2        2.5
89111111111[7], 89112222222[3],89113333333                   3          5
89111111111                                                  1
89111111111, 89112222222,89113333333[4]                      3          4

SQL> 

regexp_count(phones,',') = length(phones) - length(replace(phones,','))

length(regexp_replace(phones,',*[^,]+,*','X'))