Start off by picking up the loot dropped by the defeated enemies. Then, select the newly unlocked Interdiction from the ability menu (TAB button). Stand in the circle shown on the above screen and press the middle mouse button to summon the Dead Lord.
[TIP: If you don't wish to complete the exploration of Phariseer's Tomb but instead want to focus on the main storyline, you can leave this location using fast travel. I, however, recommend penetrating the whole tomb, especially since it won't take much time.]
Go towards the grates at the edges of the arena. Target the pressure plate shown on the above screen and press the middle mouse button again. It will communicate to the summoned Dead Lord to go there and press the plate in order to unlock the arena exit.
You can now go back to the lift. Don't use it, but jump down where the screen shows, thus returning to the first floor.
Head towards the lift shaft, which is where you've placed the pillar. Take the south door you see on the screen to begin the exploration of the unknown section.
Approach the new summoning circle and use Interdiction to call the Dead Lord again. Then, approach the closed grate and send him to the pressure plate. You can now head to the south chamber.
There, take down Mummies without a sweat. Destroy every weapon rack, too, (the above screen) because they all hide valuable items.
After examining the whole chamber, look around for a shadowbomb and use it to detonate the nearby yellow formation. Take the newly unlocked passage, jumping down to the bottom floor of the tomb.
In the basement, locate a new summoning circle and use Interdiction to call the Dead Lord again. Have him stand above the pressure plate shown on the above screen to unlock a passage to THREE chests in the area.
Each time you open one of the chests mentioned above, a new group of monsters will spawn. The easiest to eliminate are the Mummies, the Wraiths are a little bit harder, but the Undead Generals are the hardest (the above screen).
In case of Wraiths and Undead Generals I recommend sending the Dead Lord off the pressure plate to help you in battle. A good idea to taking on the Generals is to use the Reaper Form (the above screen); it should be enough to kill one of them. No matter the tactic, attack the Generals one by one, and dodge their attacks whenever you can. After winning all the battles, check out the contents of the chests opened earlier, and find a new Soul Arbiter's Scroll as well. You can now proceed to the [Judicator] main quest.