create table #tempphones (client_id int, clean_phone varchar(128)

delete from  c1
from #tempphones c1
where not exists (select 1 from #tempphones c2 
					where c2.Client_Id <> c1.Client_Id 
						and 
						(CHARINDEX(c1.clean_phone, c2.clean_phone) > 0 or CHARINDEX(c2.clean_phone, c1.clean_phone) > 0)
					)

alter table #tempphones
add clean_phone_length tinyint

update  #tempphones
set clean_phone_length = len(clean_phone)

delete from  c1
from #tempphones c1
where not exists (select 1 from #tempphones c2 
			where c2.Client_Id <> c1.Client_Id 
				and  
				(case when c1.clean_phone_length > c2.clean_phone_length 
				then CHARINDEX(c2.clean_phone, c1.clean_phone)
				else CHARINDEX(c1.clean_phone, c2.clean_phone)
				end) > 0
			) 

create clustered index new1
on #tempphones (clean_phone asc)

create nonclustered index new2
on #tempphones (client_id asc, clean_phone_length asc)

select * from #tempphones c1
where  exists (select 1 from #tempphones c2 
					where c2.Client_Id <> c1.Client_Id 
						and 
						(CHARINDEX(c1.clean_phone, c2.clean_phone) > 0)
					)
union all
select * from #tempphones c1
where  exists (select 1 from #tempphones c2 
					where c2.Client_Id <> c1.Client_Id 
						and 
						(CHARINDEX(c2.clean_phone, c1.clean_phone) > 0)
					)

WITH
pn AS (
SELECT
  [clean_phone]
FROM
  #tempphones
GROUP BY
  [clean_phone]
HAVING
  --COUNT( DISTINCT [client_id] ) > 1
  COUNT( * ) > 1
)
SELECT
  t.*
FROM
  pn
  INNER JOIN #tempphones t ON (
        t.[clean_phone] = pn.[clean_phone] )

IF OBJECT_ID( 'tempdb..#tempphones' ) IS NOT NULL
  DROP TABLE #tempphones
;
IF OBJECT_ID( 'tempdb..#phones' ) IS NOT NULL
  DROP TABLE #phones
;
CREATE TABLE #tempphones ( [client_id] INT, [clean_phone] VARCHAR(128) )
INSERT INTO #tempphones VALUES
( 1, '123456 12345678' ),
( 2, '123456 23456789' )
;
WITH
x AS (
SELECT
  [client_id],
  -- заменить пробел на символ разделителя телефонов
  [xml] = CONVERT( XML, '<i>' + REPLACE( [clean_phone], ' ', '</i><i>' ) + '</i>' )
FROM
  #tempphones
)
SELECT
  [client_id],
  [phone] = n.value( 'text()[1]', 'VARCHAR(10)' )
INTO
  #phones
FROM
  x
  CROSS APPLY x.[xml].[nodes]( '//i' ) t( n )
;
WITH
pn AS (
SELECT
  [phone]
FROM
  #phones
GROUP BY
  [phone]
HAVING
  --COUNT( DISTINCT [client_id] ) > 1
  COUNT( * ) > 1
)
SELECT
  t.*
FROM
  pn
  INNER JOIN #phones t ON (
        t.[phone] = pn.[phone] )

SELECT * 
FROM #tempphones c1
WHERE EXISTS (
		SELECT  1 
		FROM #tempphones c2 
		WHERE  
			c2.Client_Id <> c1.Client_Id	AND
			c2.clean_phone	LIKE '%' + c1.clean_phone '%' COLLATE Latin1_General_100_BIN2
	      )