There are five new quests for each faction with this phase. The bosses I promised you’d be able to fight appear to be inactive at this point. Let’s go ahead and expect those for phase 4, shall we?
Right now you should be able to pick up two new quests – A Gathering in Outland and Show Me Your Papers. The former simply requires you to visit Thrall / Gavan Grayfeather at the Throne of the Elements in Northeastern Nagrand, the latter is a 4 part quest chain.
Quest 1 – Show Me Your Papers
Head to Orgrimmar’s / Stormwind’s main gate to find lots and lots of npc’s. Use the Proclamation: 
Speak with five Citizens who still have the green title above their heads. Untitled ones don’t seem to work. Note – you’ll be immobile for a few seconds after speaking to a citizen.
Quest 2 – Arrest the Infiltrators
Use the Shackles 
on five infiltrators. These can be found all over town.
Once you’ve shackled five infiltrators, bring them to the Ring of Valor / The Stockade.
Next, you must speak to a detained Cultist, again in the ring of Valor / The Stockade, where you dropped the cultists off.
Quest 3 – Back Under Cover
Equip your Cultist’s Robe 
and head to Jaggedswing Farm / Mirror Lake Orchard. Speak with Overseer Sintak / Sylandrato receive the Book of Incantions. Visit the altar where you’ve summoned the image of Cho’gall previously and use the book.
Return to the Overseer for the next quest
Quest 4 – I Said the Words
Visit the three cultist summoning circles in Orgrimmar/Stormwind and use the book there. These circles are shown on the map one by one. Check the image below to see all of their locations in Orgrimmar. Sorry, I don’t have one for Stormwind 
.
Lastly, here’s what the circles look like:
That covers the quests for this phase. Enjoy!