Use need to spell out the name 'Phar'Ahkt' in order to summon him. To do this you must use the following runes, obtained from looting the corpses of mummies in the Living Tombs and the Sinking Sands, on the monolith in this exact order. If the order is not followed precisely then you will lose them and have to find new ones:
phar and tal can be bought/traded, but the rest are No Trade and must be looted
Ask Phar'Ahkt "What is the Ewer of Sul'Dae." (the 6th speaking point presented) then "Where is the Ewer of Sul'Dae?"
Each player in a group must place their own runes in the monolith to get the update.
Warning: If you pick the "I have no more questions. You may go." option, Phar'Ahkt will despawn, and anyone else with you who inserted their runes already will lose their chance to get quest completion.