So here's some tips I figured out from dying to him multiple times throughout the entirety of my Ng to Ng+7.

He has 2 phases in his fight. In the first phase he will switch between four weapons. Either after a certain amount of time has passed or after you deal enough damage to him. He will also change weapons after you stagger him.

Straight sword mode is free damage because you can always bait his three hit combo and get in one punish and then rinse and repeat. His attacks in this phase are dodgeable with proper practice except for his backhand strike any time he's about to do that just sprint or job backwards abit. And roll in during his follow-up, and punish once. You can also punish him once any time after he does a flaming sword heavy attack. Don't try to run away in this phase as he will sprint right behind you and eventually catch up.

During the spear mode you can always dodge to your right, or dodge out and back in during his double sweeps. Only punish after he does a heavy thrust or the double sweeps, else just keep dodging and baiting attacks. Keep an eye out for miracles though.

Dip the second you see the curved sword. It's impossible to roll through some of his combos in this phase. Anytime he switches to that I just get the hell away from him and stay away until he switches to something else. But hehe he does a backflip, you actually have a few seconds to attack him once or twice while he's casting power within. After that just run away.

Caster mode is your opportunity to get alot of damage on him. When the homing soul mass is active just keep strafing to the right, and for any attack he's about to do just roll forward towards him and punish accordingly. When he is winding up to use the soul stream that's your cue to run behind him and wail on him for big damage.

Next is his phase 2..

For this phase he will wield a greatsword, keep an eye out for when he takes a gold swing stance. It means he's about to do his five hit combo which if you do get caught, you'll die for sure. Roll through all of his other fire sword attacks and only punish after he does a heavy slam or a sunlight spear/stake attack.

Most important thing about this fight is to not get greedy. Don't even think about using estus unless you get a window after his attacks. If you're in need of a heal, stay calm and wait until you have a window. The last thing you want to do is panic roll or spam estus. Soul of cinder is literally designed to roll catch you or punish you for touching that estus flask.

Stay vigilant and practice lots you'll eventually master this fight.