Trial of the Crusader 5

Phase 2: Run, Period.
Once underground, the raid needs to get as far away from Anub'arak while keeping a patch of ice between them and him.
Anub'arak once again uses Impale, but he will chase a specified target this time. Players targeted by Anub'arak will have a mark similar to Hunter's Mark above their heads. Anub'arak' spikes speed up the longer they are uninterrupted by a patch of ice. This phase ends after a certain amount of time, not the number of times Anub'arak will have to crash into the ice patches. If you want to practice for hard mode, kite the spikes around.
Throughout this phase, Swarm Scarabs will spawn around the raid. Everyone should attack these adds even if they're not a tank. Swarm Scarabs don't hurt a lot, but they have a stacking damage-over-time effect that really hurts once you reach 3 or 4 stacks.
Once the timer is up, it's back to Phase 1. Kill the Swarm Scarabs before going back to Anub'arak.
If you don't want him to enrage, Anub'arak should only go into this phase twice.
Phase 3: They'll Crawl All Over You
Once Anub'arak reaches 30%, he'll cast Leeching Swarm. There will be no more Nerubian Burrowers for this phase so you won't need the Frost Spheres.
Anub'arak will heal himself for 10% of the current health of each raid every second for this phase until his death, so DPS will need every skill they can muster. If your DPS can't keep up with Anub'arak, let their health drop to 75-50% to reduce the health drained by Anub'arak.
And with Anub'arak down, the Heroic version of your raid is unlocked.