How should I act to my step sister when she treats me like this?

Okay me and my step sister, havent really been getting along. We are 2 years apart and she acts like a total *****! After I came home from school I started to do my homework and she was on the phone talking to her grandma and she starts yelling at her grandma and my stepmom tells her plenty of times to stop and my stepsister says "no" and my stepmom said "why would you say no to me?!" and stepsister said "because you never ground me!" and my stepmom said "i will take your phone away now" and my stepsistester said "you never take my phone away so stop". I think that is a whole bunch of ****, and shes right she never gets grounded and its not fair. My stepsister gets more then me, and gets treated better, and she gets to do what she wants when she wants. She calls me a *****, annoying, just mean words that really hurt me. And even my other sister thinks that shes being mean. I mean just because shes 2 years older then me doesn't mean she has any right to treat me mean. What should i say to her next time she starts yelling at me? And I dont treat her this way at all. I think shes a sellfish spoiled brat. Her Dad gets her anything!! And me and my sister have like nothing that she has, and she doesn't share what she has with us. But when she wants something of ours, we let her borrow it! Ugh,, she irritates that crap out of me. What should I do?! And what do i say to her!?! Thanks for any answers! And sorry this is soooo longg.