CustP
CustID  Fname      Lname        Phone
100     John        Doe         1234567890
200     John        Doe         1234567890
300     John        Doe         NULL

CustS
CustID  Fname       Lname       Email
100     John        Doe         NULL
200     John        Doe         a@a.com
300     John        Doe         a@a.com

drop table #AllCustomer
select cp.CustID,cp.Fname,cp.Lname,cp.Phone,cs.Email,
ROW_NUMBER() over (order by cp.Fname) RN
into #AllCustomer
from CustP cp
inner join CustS cs
on cp.CustID =cs.CustID

 --Combining the customer and matched customer into a temp table
   Select   A.CustID CustID,B.CustID MatchedCustID,
                A.Fname FirstName,
                A.Lname SurName,
                A.Phone Phone,
                A.Email Email,
                B.Fname MatchedFirstName,
                B.Lname MatchedSurName,
                B.Phone MatchedPhone,
                B.Email MatchedEmail
                into #AllMatchedCustomers
                from
                #AllCustomer A
                inner join
                #AllCustomer B
                on
                (
                    A.Fname=B.Fname
                    and A.Lname=B.Lname
                    and A.CustID<>B.CustID
                    and A.RN<B.RN
                )
                where
                A.CustID<>B.CustID
                and
                (
                    (
                        (1  =   case when isnull(A.Phone,1) in (isnull(B.Phone,2))
                                    THEN
                                    1
                                    else
                                    0
                                end
                        )
                    )
                    OR
                    (       A.Fname=B.Fname
                            AND
                            A.Lname=B.Lname
                            AND
                            isnull(A.Email,'A')=isnull(B.Email,'B')
                    )

                )

CustID  MatchedCustID   FirstName   SurName Phone   Email   MatchedFirstName    MatchedSurName  MatchedPhone    MatchedEmail
100 200 John        Doe         1234567890  NULL    John        Doe         1234567890  a@a.com
200 300 John        Doe         1234567890  a@a.com     John        Doe         NULL    a@a.com