It sounds like you need to firm up your boundaries so your XWW’s tantrums will be less intrusive in your life. Switch to text/email only, and don’t respond to anything that doesn’t concern your daughter. Consistency is key. Any reaction from you that is not completely devoid of emotion will only encourage her to continue In the meantime, if she does persist in calling, there is a great voicemail to text service that you could use to screen your calls. It’s about as accurate as voice recognition software can be, but accurate enough that you can say, “oh this is all bs” and delete without having to actually listen to her hysterics.
Also, I hope I am not out of line in saying this since I’m not a parent myself, but if you trust your ex’s abilities as a mother, maybe learn to turn the phone to silent from time to time. Unless you have reason to believe your daughter is in danger, there are very few “emergencies” that can’t be handled by a capable adult.