The only issue I have with the ruling on the Phantasmal Force spell was how quickly the weretiger(?) was able to realize to use an investigation check. The way I think of illusions vs phantasms is that illusions are more like holograms like seeing Tupac perform at Coachella. Interacting with the illusion will give you immediate clues that something is amiss.
I consider a phantasm to be more of a hallucination, like something a schizophrenic would imagine. The hallucination is so strong that a schizophrenic would hurt someone or themselves if necessary to act accordingly with the hallucination. It's perceived as much more vivid and "real" to the person affected than an illusion, so much so that even in the spell description, the person will try to use logic to explain the illogical like falling off a bridge that's not really there.
If the situation was reversed and you had cast Phantasmal Force on one of us, you wouldn't expect us to immediately investigate the object/creature. It would require some prompting at least, most likely from a fellow party member telling us it wasn't real. I feel there would have to be some notion of doubt inserted into the situation first before an investigation check would be warranted. Since the weretiger was alone (I hope) and there had not been any prompting yet, I was hoping to get at least a round or two. Like, maybe, when he sees Gorbug walk right through the flames and try to whack him, he would think something was up. Because, I'm sure if some wizard cast a flaming cage around me, my immediate reaction wouldn't be "Hey, let me take a closer look at this fiery infernal of a prison."
That being said, you did roll with disadvantage and still were able to beat it on straight rolls. So it wasn't easy and you did roll well. Can't really complain about that.
On a slightly separate note, I'm finding illusions to be pretty fun. How come we never seemed to use them much in the past? Gnomes definitely know where the fun is. Half cup joke, full cup of awesome.
