INSERT INTO phonebook SELECT
 [phonenumber],
 [firstname] ,
 [lastname] ,
 [company]
  FROM #tmp

DROP TABLE #Tmp

/*     Set up the test table */

Declare @phonenum table (phone varchar(10), pdate int)
 
insert
into @phonenum (phone,pdate)
select 1,1 union all
select 2,2 union all
select 3,3 union all
select 3,2 union all
select 4,2 union all
select 5,1 union all
select 5,7 union all
select 5,3 union all
select 5,1 union all
select 6,1 

select 'original table', phone, pdate 
from @phonenum
order by phone, pdate

/*  copy the non-dups from the original table based on oldest date */

select phone,pdate
into #temptab 
from
(select p.phone,p.pdate
from @phonenum p 
	join @phonenum p2
    	on p.phone = p2.phone  
GROUP BY p.phone,p.pdate  having p.pdate = min(p2.pdate)) t
 

select 'temporary table - non-dups with oldest date', phone, pdate from #temptab
order by phone
drop table #temptab

select phone , pdate  
into #temptab 
from
(select p.phone,p.pdate 
from @phonenum p 
	join @phonenum p2
    	on p.phone = p2.phone  or p.phone is null
GROUP  BY p.phone,p.pdate  having p.pdate = min(p2.pdate) or p.pdate is null or p.phone is null) t