You need to start doing damage really hard by using your ultimates and thresholds. Watch out for the KO Acidic Spiders that will spawn from the green splat Araxxor spits out. If they touch you, you're dead! The KO Acidic Spiders will have a bar that's gaining adrenaline above their head. When it reaches full it explodes.
Getting Araxxor down to 10,000 life points then luring the Acidic Spiders into him by running across Araxxor. Araxxor will build up rage and start hitting you harder so we recommend barricading after luring all 5 Acidic Spiders. He should be at about 30,000 life points, hurt him hard till he drops to 5,000. Sip your Saradomin Brews throughout the Phase. Try to keep your food till Phase 4.
It is wise to sip the Saradomin Brews after you have used ultimate while you are regaining adrenaline to use thresholds. You should use a restore after you are at 50% adrenaline with a decent amount of health and you should start using thresholds. You can always use 1 threshold first after the ultimate, then devotion, then another. Araxxor will cleave you this phase too.
On week 2, when the middle and right paths are unlocked, on phase 3 there will be shines of light coming down. To avoid the spam 300 damage hits when Araxxor makes the room dark, you'll need to step into these shines of light!
If you don't lure the spiders on Phase 3, Araxxor will obtain a buff on Phase 4. We advice luring them at around 10K health because he increases in rage when you lure them into him. After Phase 3 has ended, a cut scene will play.