Why does Margo use Q's cell phone and what does she do when she hangs up from the call?

Margo uses Q's cell phone to call her mother, who immediately tells her that she changed the locks. Margo speaks to Ruthie and apologizes for not telling her where she was. After the phone conversation, Margo screams with anguish at how self-centered her mother is and reiterates how she felt like she had to leave.