Knew what he was doing, he was protecting his mom from her tormentor.

Phil was up to all kinds of no good.

If you watch again you'll see that Peter, who was studying medicine, collected the leather for the rope from a cow that had died of anthrax. He knew what he was doing. There was nothing involuntary about it. The movie leaves you wondering who the real villain was.

but yeah, def not only intentional, but most premeditated.
2nd watch i picked up all the mentions of anthrax.
i think i spent most of the 1st time waiting for all bloody hell to break lose.

My focus was on the long game being played by Peter as he had no way of knowing how things would unfold. He didn't cause the cut on Phil's hand. He was not involved with the selling of the hides which created a demand for the deadly ones he procured. He didn't ask Phil to make a rope (at least I don't think he did). A lot of dominoes fell into place which were beyond his control for Peter to enact his revenge. Ultimately, he seemed to me to be a resourceful, smart and opportunistic man which swayed me to the murder determination. The film certainly offered a very interesting character study, not the least of which was the subversion of the internal and external thoughts and motivations of the two men.

kept my eye on whether they were gonna get together, or whether he was placating him.
but searching out that cow was quite the deliberate act.

What was also clear to me, based on the seemingly unmotivated animus between Phil and Rose, especially the musical sparring, and some things Phil told Peter about his dad, that Phil had had a relationship with Peter's dad and Rose blames Phil for her husband's drinking and suicide, while I think Phil blames Rose for the same things.