How to check phone number for each employee is different

--for existing data
select * from table1 where MobileNo in -- fetch whole row having same numbers
(
     select mobileno from table1 group by  a having  count(*) > 1 -- fetch mobileno list which are repeated
)

'on textbox leave event
       Dim exist = DBGetData("select count(*) from tabel1 where mobileno='" & txtmobileno.text & "'")
       If exist > 0 Then
           'show message not allowed
           'empty Mobile number textbox
           'focus txtmobileno
       End If

create procedure check_contact_No
	@parameter_entered_contact_num as varchar(50)
as
begin
if(not Exists(select ad_contact_1 from admin_user_profile where ad_contact_1 = @parameter_entered_contact_num  ))
if( Exists(select ad_contact_1 from admin_user_profile where ad_contact_1 = @parameter_entered_contact_num  ))
	select COUNT(*) from admin_user_profile 
else 
	select COUNT(*) from admin_user_profile where ad_contact_1 = @parameter_entered_contact_num 
end

'on textbox leave event
       Dim objcls As New database_Connection
        Dim da As New OleDbDataAdapter
        Dim ds As New DataSet
        Dim cmd As New OleDbCommand
        Dim con As New OleDbConnection
        Dim flag As Boolean
        Try
            con = objcls.GetConnection()
            cmd.CommandType = CommandType.StoredProcedure
            cmd.CommandText = "check_contact_No"
            cmd.Parameters.Add(New OleDbParameter("@parameter_entered_contact_num", txt_contactno.Text))
            cmd.Connection = con
            da.SelectCommand = cmd
            da.Fill(ds)
            If (ds.Tables(0).Rows.Count = 0) Then
                'show message not allowed
                'empty Mobile number textbox
                'focus txtmobileno
            Else
               'number is unique
               'do your coding
            End If
            Return flag
        Catch ex As Exception

        End Try