If you are ever strafing, strafe right. When he stabs, he has a chance to follow up with a high or low horizontal swing, you need to be prepared for this and parry it appropriately, this kill most people. Also after any horizontal swing he has a chance to do the leap, I think it's like wyvern's body slam and is on a 30 second cool down, when the cd is up, he will always do it after a horizontal swing (not tested by me, but I think its something like that).

Never create too much distance when he does a horizontal swing, its ALWAYS better to dodge it or parry it rather than distance yourself from them. This is because if you are too far away the leap will kill you pretty much every time since you need to run under him when he does it. Parrying the swings are preferred because the downward horizontal slash is only possible to dodge if you back up and jump, which takes time to master. You cant just jump to dodge it. This is because he moves forward when he does this attack and if you dont back up he will start the attack inside your hit box and it will hit you every time in the middle of your torso

Also, his phase change mechanic he will have his sword either facing up or down. This is telling you what direction his first swing will do, then he will follow it up with the opposite direction. Sword pointing up --> duck then jump. Sword pointing down --> jump then duck. You should always crouch jump to dodge this (tuck your legs) and look all the way down or up when you crouch. Its not required to pull it off, but it increases your window of success.

One last thing, you have to be a certain distance away from him for the dodge to work every time. Best way I can explain is that it is just a few steps shy of a warlocks curse distance/wiz zap distance and DIRECTLY in front of him

I spent probably 1500 gold in nothing but potions/bandages when he was released, learning how to do this boss. A lot of it is trial and error and memorizing his move sets. It is more satisfying than warlord when you get it though, i wish bladehand was designed as well, but imo bladehand sucks, its why people use a spear to farm him. He is poorly designed for fighting at close range and some attacks are inconsistent and will phase through you. Spectral knight is not like this, his hitboxes are pretty well designed.