First phase, learn moveset and attack 1 to 4 times during openings. Just sprint but stay close enough that monke doesn't feel the need to charge at you. Firecracker is op here. Second phase, deflect every attack and avoid perilous.
Don't get fooled you can deflect every melee attack in phase 1 except grab. Initially phase 1 was pain for me too because when i first saw a huge ape my mind switched into souls mode. I ran like an idiot and thought of parrying never came in mind because its so irrational to parry huge ape hands. Then i realized every damn attack can be deflected and the grab is actually a sweep then it turned from an soul boss to sekiro boss. So its better and faster to fill its posture than to deplete vitality in phase 1.
Yeah, how do I dodge the grabs because I keep trying to dodge them at close range and I do but then i get sucked back into the hitbox and just die immediately
His grab attack is broken, just like a lot of other mechanics in the game. If the back of his wrist grazes you, that's a successful grab and you are now dead.
Or alternatively bait the poop attack, stay far enough away and he'll stick his hand behind him, that's your cue to make a mad dash towards him, get behind him and slash 2x then firecrackers (can be bought from a merchant on a high cliff top above the house where you get the memory bell) and hit 5x rinse and repeat till deathblow. For phase 2 parry 2 slashes and he should stand up and drop use your loaded spear (can be found in house at ashina reservoir you need the gate house key from the guard on a bridge) and pull out the centipede then back up to avoid his screeching, wait for him to rush you and do that over and over till he dies.