I'm so upset. My sister lost her phone a few months back

And she uses our mum's. So today something happened and in some sort of a rage she took my phone without asking me and took off to her therapist.
I need my phone right now. I called her and told her to come right back with it, to which she unapologetically stated that I could borrow our other sister's. Later, I called her again, multiple times, and she didn't pick up. It's so hurtful, to be used in some sort of entitlement to someone else, just because most of the time I'm not an asshole doesn't mean my own blood gets to treat me like shit. And she knows that we can't fall out because it would only be to the delight of our mother. So in that way I'm checkmate, I rely on my sisters emotionally and for company. So she's misusing that. I feel like putting up quite the fight when she returns home. But a part of me feels like it would only make things worse.