Phase 1: Above Ground

Pull the boss, position him and use 2 DKs to deathgrip frost spheres on both sides of Anub. There should be 2 ranged dps assisting both DKs with killing the sphere. If you have 3. DK its good idea to have him on standby incase the grip bugs and other sphere only drops halfway down. These 2 frosts should not be destroyed at any point of the fight.

Use 2 Offtanks. (I suggest using paladins and warriors as blockvalue reduces damagetaken a lot.. and holy wrath / shockwave can be used to interrupt ) One on both side ready to pick up the Nerubian Burrowers and to take them on top of the freshly dropped frosts, as close to Anub'arak as possible, but still keeping (12yard?) distance between addpacks so they wouldnt get 3 stacks of haste increase.
Offtanks have to be ready to interrupt shadow strike with aoe stun/silence as soon as its cast. All burrowers cast it at the same time.

Challenge of the first phase is having enough AoE dps to take Burrowers down way before next wave of them spawns, so tanks have time to drop their debuffs and go pick up the next wave. For the AoE to be effective enough all 4 adds have to be kept in the range of AoE, yet keeping them far enough so you dont have to deal with 1 second shadow strike casts. How to reach that necessary AoE is all about the people you have available. Unholy DKs, frostfire mages, rogues and fury warriors are somewhat awesome.

10 seconds before Anub burrows maintank should move him to the left side of the room to avoid losing frost paths unnecessarily.

Phase 2: Submerge

P2 begins when Anub burrows. He will target a random player in the raid and that player has to immedialitely start running towards south. Especially melee dps has to be awake at this point as you dont wanna lose those 2 death gripped frosts. Second wave of Nerubian Burrowers are still up at this point and DPS has to finish them up.

As previously mentioned the kiting begins with the first target running to south. When he's far enough he stops running and waits for the spikes to reach him. You should have BoP rotation ready from your paladins, so the paladins whos turn to BoP is there in range ready to BoP the kite target. At the same time some of your ranged dps should be dropping down 2 frosts on the ground. Burrow target will run to either of these to reset the spikes. When its reset Anub will pick up new target and that target has to run south, wait for BoP and run to frost. There will be 3. kite target after this, but if you've done the kiting right with first 2 he only has to kite for 10 seconds or less and doesnt need to use BoP or ice. His job is basicly to start kiting the boss towards the tanking spot. ( just dont destroy tanking frosts )

Meanwhile rest of your raid is watching out they arent in the kiters way and are killing Nerubian Swarmers that spawn all around the room. These adds target someone in the raid and try to reach him. If they do they start stacking a nasty debuff that ticks 1.5k for each stack every 3 seconds and lasts 1 minute. Don't let them hit anyone. You can use stuns and slows on them unless they enrage which gives them immunity. (tranq shot should remove the enrage)

Challenge of this phase: Kiting long enough. You may not use more than 2 frosts for this phase, otherwise you will run out for next time. So wait for your BoPs to be nearly over before you go reset. Make sure you only drop 2 frosts, and that both of them are used in this phase. If not next time you enter phase 1 the adds will be harder to pick up as one of them is most likely slowed somewhere.

After being 3 times in P1 and twice in P2 you should hit P3.

Phase 3: 30%

P3 begins when Anub hits 30% hp and starts casting Leeching Swarm, its clearly the hardest phase of the fight. Simply for this phase you have those 6-7 healers in the raid. Your DPS and Tanks will keep on doing what they were doing p1. Dont panic.

What makes it hard? Due the nature of leeching swarm everyone in your raid, except tanks, has to be kept at around 1k HP. No more, no less or the boss starts healing too much. Low health combined with Penetrating Cold debuff is pretty tough shit.

Penetrating Cold is a dot-debuff that Anub casts on 5 raid members. It lasts 18 seconds, ticks every 3 seconds for 6k frost damage.
So when a new wave of Penetrating Cold debuffs are being cast you have 5 people in 1k hp that need to be get to that 6k+ health in a few seconds. This debuff is there also in P1, but its wasnt worth mentioning as its harmless when people have full hp.

To keep raid up from leech everyone in the raid needs to be healed for atleast 250 hp / second. For melee this is easy as they will stay alive just by hitting Anub that should have Judgement of Light on him. JoL keeps the melee alive by itself. Ranged and healers need some additional healing as they cant benefit from JoL. You can use Healing Stream totems and Vampiric touch to keep one group alive and have a restodruid rolling rejuvenation on the rest. (rank 10 is enough)

Each of the Penetrating Cold targets needs to have his own personal healer that makes sure he stays alive for that 18 seconds. Addon called Penetrator helps a lot by marking each of the Penetrating Cold targets by a raidmark. ( X or Star, Square or Circle, Moon, Diamond and Triangle ) Be shameless and just top your healing target. Yes it makes the boss heal a bit more, but as Penetrating Cold only has 16 second cooldown its possible you already have a new target to heal before previous ones debuff has ended. If you have the old target in high hp its more likely you have time to heal the new target and both targets will survive.

What every raid member should do is to help the healers. Your healer might be busy and not able to push enough HP to you before Penetrating Cold ticks for the first time, so all raid members should help out by popping Frost Res Potion when they are targetted by Penetrating Cold the first time. If they are targetted second time they should use Healthstone. Rogues, Mages and Paladins should use their personal cooldowns to remove the debuff.

Also note that tanks are taking brutal damage from the leech combined with melee hits. Holy Paladins are simply great for healing the tanks in last phase.