Actually I think the grandparent comment should be read "...proof [of the truth] of any phenomenon..."

I suggest the problem is with the concept "true".

The assumption that all phenomenon have a physical basis is exceedingly practical and produces fantastic predictive success. "True-ness" as it is intuitively defined is not interesting in this case, indeed it may be nonsense.

Stated another way, if we're going to describe "true" as some aspect of reality that we can never directly perceive but only get at through fallible senses and perceptions then we are not only flirting with something that is likely a-priori unprovable but also likely very uninteresting.