How do I deal with an employee with zero boundaries regarding calling outside of work

Okay I recently became a manager at my work and I have an employee who is extremely anxious. I spent two weeks reassuring her that she is not getting fired (I genuinely don’t know why she was convinced of this when both of her managers kept telling her it was okay) and she is convinced that everyone is rudest to her and that she does the most work. Anyway she calls me fucking constantly and I don’t know what to do???? It’ll be when neither of us are at work or when I’m at work and she isn’t or vice versa. And when she does call she complains at me about work for a fucking hour. It’s genuinely making me feel like I don’t go home at night because this person is blowing my phone up. I try to not answer, etc but then she’s just frustrated when I get back to work. Idk what to do. Any suggestions???