For me, the biggest part of learning to set better boundaries has been to recognize when I need to let them just be pissed off. Not my job to soothe her every ruffled feather. If she has such a big issue with communication while you are at work, honestly, that's her problem, not yours. You don't have to solve it for her. She can get pissed or not, you need to let go of worry about how she reacts, and just focus on what's right for Cipher.
Now, when the inevitable escalation of anger and raging happens, realize she is trying to break down the new boundary you are erecting. Hold it. Let her burn the house down in anger if she wants.
If she is busy and I had not either replied or initiated a text or email she gets angry and says I am purposely ignoring her. Never mind that I am busy with work. She hates the excuse. She say I made an agreement to reply in at least every 30 to 40 minutes.
She's trying to set you up to be a liar or the bad guy for breaking your word with this stuff. Here's the thing, she's going to one way or another in her own mind. So why worry about it? Do what you need for you. Like do your job and turn off the phone to prevent the distractions.
If you feel you need to say more to her, regardless of what's been said before, just tell her it doesn't work, too intrusive, too distracting, and you're not going to respond like that anymore.
The next thing becomes when she unleashes her crazy barrage at you in response, what are you going to do then? In the past, it has always broken you down and you've caved. You need a plan of something different to do. Leave and go to a bar to hang out. A friend or family member's house. But like breaking any other habit, if you don't build a new habit to replace the old, the old will simply come back. Pre-plan what you are going to do, how you will react, and then follow through and do it. And remember it will be hard, she's going to be going berserk while you're doing it. So it's got to be something that is quick hitting, something she can't interrupt.
Leaving and letting her have her breakdown is honestly the only thing I've ever seen to work, by the way. There might be other ways. I don't know them and have never seen or heard anyone else say anything else that worked.