Generally at some point a person wants to get some goods and services from their neighbors and barter only goes so far.
The fact that you are in a society with 330M other people who all use the same "imaginary" currency makes it incredibly sticky.
Exactly what I said. It's imaginary, just that it's a collective imagination.
At some point these things we conjure up out of our collective imagination are every bit as real as the ground hitting you if you jump off a building.
I.e. imaginary.
Your phone bill is just another level of abstraction on top of the USD imagination.
In the middle ages witches were believed to be real by enough people to burn them on the stake. The full power of the state was behind this. Unless there's scientific evidence of sorcery now I think witches are imaginary.
It doesn't make the burning sensation less real.
The value of cryptocurrency is just far more imaginary than dollars, euros, or even gold.