I call this part of the ritual 'calling the Goddess' because that's what I do. Some people call this part 'invoking'. I call it 'calling' because I have a different way of working.
Because I believe that we are all a part of the Goddess, I don't feel the need to invoke beacuse she is already a part of me. However, I still want her to be involved - it's like calling up the rest of the world to come and help.
I call the Goddess to watch my ritual and help me when I need it. I imagine that she's sitting inside the circle but near the edge, in the same direction as the altar.
So this is my way of doing things, feel free to do what you think:
'Goddess, I call you to witness my rite. Hail and welcome!'