I need advice (idk why im putting this on this site...)

I hope this doesn't get taken down bc im really desperate. My sister has been playing this game for a few years and she was 13 when she met a 20 year old Indian guy on there she told him she was 17 WHICH IS STILL A MINOR, that didn't stop him from getting involved with her romantically. Fast forward 2 years later(now) they're texting and sending photos to each other. She still tells him she's 17(his dumba** didn't realize). The red flags (i mean there are a lot so far) are this guy is very possessive and even made her delete her main instagram account bc he didn't want other people following her. He's also homophobic/transphobic and filling my sister's head with gibberish. HE ALSO GOT HIS PHONE STOLEN IN WHICH HE HAD MY 15 YEAR OLD SISTER'S PHOTOS (not nude just selfies). guys im really scared for her i feel like a disappointment. My parents will never confiscate her phone bc she throws a tantrum. What do i do?!

UPDATE: THE GUY KNOWS SHE'S FIFTEEN AND HAS TOLD HER THAT HE DOESN'T THINK ANYTHING'S WRONG WITH IT. I'M CRYING HOW DO I SAVE MY SISTER?!!