Monsters don't have the Surprise ability. Surprise was a condition associated with encounters only ("A monster surprises you").
Thanks Tibs - that makes better sense. I am guessing Ambush was the attempt to bring it to monster abilities, though it plays out much differently? I always preferred the Surprise mechanic, though it might be difficult to implement for those same phasing reasons.
I am guessing there are very few Surprise encounters, if it was only done for the original edition of Pharaoh?