What do you do when your mother-in-law yells at you?

You do not describe any medical illnesses, so I can't address this question thoroughly. However, if she is just yelling at you, when you do hang up tell her you do not appreciate her yelling at you and you are doing your best to help her. Sit down and discuss what her needs are and then tell her what YOU are willing to do for her since you are not required to take care of her. Where is her son (your husband) in all this? Why doesn't he speak up for you? Do not allow yourself to be bullied by your mother-in-law nor your husband. Stand up for you!

ANOTHER ADVISER SAYS: Do not involve your spouse

You may think the best person to manage a tough mother-in-law would be her own son, but asking your spouse to step into the middle of a conflict can be problematic.

"In addition to being insulted and hurt, often the wife feels completely unsupported in her feelings, so her husband is caught in the middle," says Radcliffe. "He loves his wife, he loves his mother and, especially if he's young, he's not particularly skilled at negotiating those relationships, so he makes his wife feel like she's doing something wrong." This is a lot of pressure to put on your spouse and, Radcliffe says, as an adult, there is no reason you can't manage this relationship on your own.
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Personally I'd throw her under the bus

Curious, what was it that your mother-in-law needed help in that was so urgent that she needed to yell?

I understand she is not your Mom, but if the shoe was on the other foot and it was your Mom and your husband made the comment "she's not my Mom", I bet you would find that to be very hurtful.

Thanks so much I appreciate this

Speak with your husband about HIS mother's rudeness... You are the only one who can change your situation..

You don't mention your mother-in-laws age but it sounds like she may have dementia. I had a good relationship with my mother until I had to become my parents' caregiver. Then everything went south and mother began yelling at me like I was 5 years old. She had been diagnosed with Parkinsons Disease which causes pretty severe dementia but she was in denial that anything was wrong with her. For a while I did not understand her rude behavior was neurological and I took everything personally. When I got her and Dad in an Assisted Living Facility, they gave her an anti-psychotic drug which helped her immensely. If I had understood dementia earlier I would have realized she was depressed and not attacking me personally.

Has your relationship with her been pretty good over the years? If this rudeness was an exception, I'd chalk it up to every one is entitled to have a bad day now and then.

She told you to "get out" -- are you living in her house? Or what is your caregiving arrangement?

If this is not just a rare exception, then if you can explain your situation in a little more detail we will be able to give you more specific responses.