I'm going to tell my sister I'm not going to keep my phone on, even on vibrate, when I'm at work
Why would you tell your sister this about your phone?
So that she won't disturb me when I'm working.
It's okay if you want to enforce boundaries with your siblings while at work. A workplace is meant to have a certain professionalism to it and your sister should understand this. Be more receptive to her communication attempts outside of work to make her feel as if you aren't just trying to avoid her.
She should be more considerate and not interrupt me when I'm trying to get work done.
It's true that your sister, or anyone for that matter, should not be bothering you while you are at work.  Let her know that it is necessary for you to keep your phone off while you are at work, and that you will get in touch with her afterwards to see if she needs anything.