If a LLM says "I am in pain", is it just stringing together words or is it feeling pain? Does pain exist for a being that never felt any kind of physical pain, never had any pain receptors?

There are humans who don't have any pain receptors because of genetic mutations. They cut themselves all the time, they bleed, they break bones and they don't seem distressed by it even on a purely mental, intellectual level.

I am not saying that everything that a LLM say is true (the human without pain receptors can also say "I have pain" without feeling any pain).

Just that we cannot exclude that LLMs can have phenomenological consciousness by a simple argument of substrate. But similarly we cannot say for sure that they are conscious.