Codependency Support Group
Codependency is defined as someone who exhibits too much, and often inappropriate, caring for another person's struggles. A codependent person may try to change, or feel shame about their most private thoughts and feelings if they conflict with the other person's struggles. If you are on a journey towards self-love, this support group is for you. Join us and find others...

Just decide enough is enough.Tell her this has gone on long enough and you don't want to do it anymore. Remember, you can't change how someone reacts to you, just how you react !
Good luck !
You have to not only set your boundaries, but enforce them. Its' not easy. And as nola points out, you can't control how she reacts. Remember that this dynamic has been around in your relationship for a long time. So don't expect a sudden change or a happy response.
You are setting boundaries which is great. it reminds me of my mother so you are not alone. You are not responsible for her behaviour and although you probably do feel guilty for not wanting to talk to her, missing calls (you a terrible person not!, how dare you not picking up the phone!!!!!!!). It may be worth while speaking to someone to help you support your boundaries... and how you feel about setting those boundaries. I have spent some time in therapy but it has been worth it. Just a thought. I ended up switching off my voicemail (I haven't had it back on for three years) as I got sick of listening to awful messages about why I wasn't answering her calls. And my mother would always call during work hours as well and got nasty if I couldn't talk to her at work. The stories go on... Well done for making the step.. it is brave but at the end of the day your Mother owns her own behaviour and issues like we own our own.
You do not need to parent you mother anymore. Some articles on Adult children of Narcissists may be confronting but a worthwhile read. Feel free to chat any time.
I too have experienced the guilt for not calling my mother or answering when she called. It put a major strain on both of us and our relationship. I used to feel so guilty, but through coda i have learned that as an adult i am entitled to a life and she hers.
About a year ago, i got up the courage to tell her that i had obligations through the week and was trying to have a balanced life. I explained that i loved talking with her but that daily was too much and i needed to take care of me. We now talk on Sunday mornings early, we enjoy our weekly talks and have so much to talk about. It has made it much less stressful and something i enjoy.
I know you will find something that works for you....remember your feelings matter too
I know my dad is priobably rolling over in his grave because of it, but I had to do it for MY sanity....
Best of luck...