The Symposiasts (Side Quest)
This mission becomes available in Alexandria after completing the Wrath of the Poets sidequest.
Speak with Phanos again for an invitation to party.
He'll head to the street and mount a horse- borrow or summon your own and follow him, discreetly preparing your favorite horseback weapons for immediate use.
You'll be ambushed en route by mission-level-appropriate soldiers, rather than the usual Alexandrian rabble. Phanos won't flee the fight, so you can't either. Ride them down on horseback, or engage toe to toe in the street.
Once they're dead, there are no other encounters before Phanos leads you back to his garden of earthly delights.
Speak with him again to trigger a surprise attack, this time a much larger force of soldiers in the front street.
Your 'goal' is to defend Phanos, but he can't be killed, only briefly downed, so just focus on eliminating soldiers.
When they've all been killed, speak to Phanos once more for mission completion.