MySQL 8.0

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select version();

version()

8.0.30

CREATE TABLE import (
  line varchar(512) DEFAULT NULL
)
INSERT INTO import values ('11111111,22222222,33333333')
select * from import

line

11111111,22222222,33333333

create table phone (
    num int
)
insert into phone (num)
select
  SUBSTRING_INDEX(SUBSTRING_INDEX(import.line, ',', numbers.n), ',', -1) name
from
  (select 1 n union all
   select 2 union all select 3 union all
   select 4 union all select 5) numbers INNER JOIN import
  on CHAR_LENGTH(import.line)
     -CHAR_LENGTH(REPLACE(import. line, ',', ''))>=numbers.n-1
order by
  n

Records: 3  Duplicates: 0  Warnings: 0

select * from phone

num

11111111

22222222

33333333

truncate phone
insert into phone (num)
with recursive
    N as ( select 1 as n union select n + 1 from N inner join import
        on n <= length(import.line) - length(replace(import.line, ',', '')))
    select distinct substring_index(substring_index(import.line, ',', n), ',', -1)
num from N inner join import

Records: 3  Duplicates: 0  Warnings: 0

select * from phone

num

11111111

22222222

33333333

truncate phone
insert into phone
select j.line
from import i
join json_table(
  replace(json_array(i.line), ',', '","'),
  '$[*]' columns (line varchar(50) path '$')
) j

Records: 3  Duplicates: 0  Warnings: 0

select * from phone

num

11111111

22222222

33333333