Well, Kos has found evidence that the CIA considered WP a chemical weapon when Saddam used it against Kurdish insurgents. From a 1995 intelligence document:
IRAQ'S POSSIBLE EMPLOYMENT OF PHOSPHOROUS CHEMICAL WEAPONS -- IN LATE FEBRUARY 1991, FOLLOWING THE COALITION FORCES' OVERWHELMING VICTORY OVER IRAQ, KURDISH REBELS STEPPED UP THEIR STRUGGLE AGAINST IRAQI FORCES IN NORTHERN IRAQ. DURING THE BRUTAL CRACKDOWN THAT FOLLOWED THE KURDISH UPRISING, IRAQI FORCES LOYAL TO PRESIDENT SADDAM ((HUSSEIN)) MAY HAVE POSSIBLY USED WHITE PHOSPHOROUS (WP) CHEMICAL WEAPONS AGAINST KURDISH REBELS AND THE POPULACE IN ERBIL... AND DOHUK... PROVINCES, IRAQ. THE WP CHEMICAL WAS DELIVERED BY ARTILLERY ROUNDS AND HELICOPTER GUNSHIPS (NO FURTHER INFORMATION AT THIS TIME).
For the record, I do not think that this means the CIA actually considered WP to be legally a chemical weapon. All that would show is that this source is incorrect on the classification of WP. Rather, I think there's a touch of sensationalism in the document (note also, for instance, the phrase "the coalition forces' overwhelming victory-- how is that adjective pertinent?): if I were a betting man, I'd say this piece was designed to convince someone to take further action against Saddam.
What the document does imply, however, is that the CIA believes the use of WP against human targets has the same ethical problems as using a chemical weapon.