That's really cute that she feels so close to you that she wants to talk to you on the phone!

I agree with the other poster about switching to text messages.  You can probably get a special plan to give you a bundle (or unlimited) texts.

She is probably bored and missing you and as much as you need to be there for her as a parent you also need to work! How frustrating!

Perhaps sit her down and explain to her that you can't take personal phone calls at work but that you love her and you really do want to be able to hear from her during the day and help her out with whatever is troubling her but it needs to not effect you work.

Does she have a mobile phone? maybe you could get her to text you instead, that way she feels she is being heard and you can answer her when it is convenient.

Refuse the phone call or have your manager tell her that it's not on and she's not to call the work number again.