Interesting but
B.Phl1_descr = B.Phl1_descr
not working but
ISNULL(B.Phl1_descr,'-1') = ISNULL(B.Phl1_descr,'-1')
works,
So just a simple change in the below code work it out
(CASE WHEN LEN(@Phl1_descr) > 1 THEN A.Phl1_descr ELSE ISNULL(B.Phl1_descr,'-1') END) = ISNULL(B.Phl1_descr,'-1') AND
(CASE WHEN LEN(@Phl2_descr) > 1 THEN A.Phl2_descr ELSE ISNULL(B.Phl2_descr,'-1') END) = ISNULL(B.Phl2_descr,'-1') AND