I have some valuable advice that will make this battle easier and also allow you to skip the second phase of this three phase battle.
Firstly go to options and turn off both Auto Lock On and Auto Switch Lock. Trust me this is a massive help not only in phase 1 but mainly 2.
Phase 1This phase is all about timing. Keep to the back and angle the camera so you can see both claws. As soon as one of the claws lowers immediately jump. Don't wait for it or try and time a dodge just jump out of the way when the claw lowers. This gives you enough to compose yourself then get two hits in(1 with power weapon). Jump to the back again and now watch for the other claw.
Provided you stay at the back it pretty much prevented the claws from using its other attacks.
Listen out for a Lazer attack. This is a double attack. When you hear the mechanism ready to fire begin jumping. Another lazer will fire straight after so jump again.
This phase is purely about timing. Don't worry if at first you get pummeled, it takes practice and understanding the movements.
Ideally you should use no more than 1 or 2 healthswitch to your power weaponStage 2Run up some stairs and you will see mechanical arms. You are supposed to destroy these, however these will eat into your health. They inflict massive damage and are difficult to dodge.
Instead run straight to the back.
Stage 3There is a small eye type mechanism protected by a cage. I found that if stand right underneath the eye it can't hit you. So stand underneath then wait for cage to open then hit it with your power weapon.
Be careful sometimes the momentum of your swings can put you into danger however you should have enough health.
According to other videos you are supposed too run from side to side of the eye. I found I lost to much health.
Here is a video
You can clearly see that as I was standing still I was not taking damage the biggest problem was the slow speed the weapon and the momentum of tree swing dragging me forward. Maybe the Vibrocutter or Staff would accutaly be more effective.