If your password is unphishable, then it is obviously the case that it can be the same everywhere. Or it wouldn’t be unphishable.
I don't follow.
Because I can't be fooled into divulging some credential where I shouldn't means that it is appropriate that I use it everywhere? Are there not other attack vectors that would drool at the thought?
Conversely, that the fact that I can use the same credential everywhere is somehow a necessary aspect of 'unphishability'?