This dream reflects that you have some distrust of your girlfriend and are worried that there are other men hiding around her.
Calling is a communication process.
Your dream girlfriend refers to your girlfriend's image and feelings.
But the person who answered the phone was a man. You are afraid that your girlfriend will associate with other men in a corner that you can't control and understand.
This is what you are worried about, because you love her too much, which causes worry and doubt.