What does Elizabeth Johson mean by "The symbol of God functions"?

The phrase used by Elizabeth Johnson is both a critique of religion in general and a commentary on the sociological idea of religion and deity. Her quote "The symbol of God functions" is intended to say, first, that God is inherently a symbol and nothing more. This lines up with the ideas of many philosophers from the 1700's and 1800's, that God is simply a human construct, designed to give us something towards which to strive and to keep us in line morally.
The second point is the identify that that symbol serves a purpose, as was similarly stated. The symbol and imagery of God serves a purpose in this world, and the way we use that symbol shapes our worldview, which religion inherently does. A prominent feminist, Johnson criticized the male-centered idea of God, implying that it alienated and demeaned women by putting the most powerful being as a man. If we adjust our speech and treatment of God, we will reshape our world at the same time.

In her classic contribution to feminist theology She Who Is: The Mystery of God in Feminist Theological Discourse Elizabeth Johnson famously states that "The symbol of God functions." What she means by this is simply that the symbol of God has a specific role to play in society. As a symbol—perhaps the ultimate symbol—God isn't just an abstraction or something that has a neutral effect; it shapes and defines what kind of society we live in and how we treat each other.
So for instance if we insist on talking of God in exclusively male terms—as God the Father, and so on—then the practical repercussions will be to strengthen the existing patriarchy. In other words, the symbol of God, as it is traditionally construed, serves to reinforce male power in society. As a feminist theologian, Johnson naturally wants to change that symbol. By changing the language we use about God she argues that we will also change the function that the God-symbol exercises in society. No longer will the symbol function to serve patriarchy, but instead validate a more inclusive society in which the voices of women are heard and acknowledged.