rank() の同じアプローチを使用してから、次のように新しい PIVOT 関数を使用できます:
with cusCte as(
select cusid,cusph1,RANK() over (partition by cusid order by cusph1) r
from #cusphone)
SELECT cusid, [1] AS C1, [2] AS C2, [3] AS C3
FROM
(SELECT cusid,cusph1,r
FROM cusCte) p
PIVOT
(
MIN (cusph1)
FOR r IN
( [1], [2], [3] )
) AS pvt;