If the ratio of duplicate to unique phone numbers is "small" AND you have a unique row identifier on the table you might be better off doing something like this...

If Object_Id('tempdb.dbo.#Tmp') is not Null Drop table dbo.#Tmp

Create table dbo.#Tmp(RId Int Identity(1,1),Phone VarChar(7))

Insert dbo.#Tmp Values('1234567')

Insert dbo.#Tmp Values('9876543')

Insert dbo.#Tmp Values('1234567') -- dup

Insert dbo.#Tmp Values('9876543') -- dup

Select * from dbo.#Tmp

Delete #Tmp

from dbo.#Tmp

join dbo.#Tmp t2 on #Tmp.RId>t2.RId and #Tmp.Phone=t2.Phone

Select * from dbo.#Tmp