You have wonderful advice. The only thing I can add is that my mother is difficult too. Firm but loving boundaries are a must. It took me 45 years!
When we spoke on the phone, I made the commitment to myself that I would only say and email kind things to her. If I felt the least bit of a dagger coming my way, she got a "time-out", believe it or not. I had a rotating five excuses in my hip pocket for getting off the phone or leaving the area. None of them were about her.....When I got that pain in my gut and knew she was on the war path I would nicely but definitively pull an excuse out and say something like, "Uh-oh, the dog is going to have an accident, I've got to go. Bye." and hang up. I wouldn't call her back for a few days, maybe a week, and I wouldn't return her calls or email. When I did, I would start with a shallow, friendly email with a recipe or happy article or a photo of the kids...something happy. Then I would call her in another day.
She is sharp (no pun, well maybe a little) and figured it out quickly. We BOTH have healed a lot from this. We have never talked about me giving her "time outs", I just have been consistent and it has helped a LOT. It has now been ten years and I feel like we have a pleasant relationship. The incidents still occur but with much less frequency. We had one recently and before that it was 2 years. This one went by in a couple of days. I sent her a loving email and was strong enough to tell her in my email that I wasn't mad at her, but thought she was at me and perhaps there was a misunderstanding. She responded well. I think she too enjoys the 'new and improved' relationship and values me more for it.
Good luck. It can be done. I agree that strong boundaries are the key. It is so hard to be loving when you are in pain, but try my tricks.
Blessings to all of you.