[TOMT] Horror movie from 80s might be late 70s or early 90s about a high schooler turn into monster

Hello, I’m looking for an old horror movie and gonna describe what’s inside from what I remember, there might be some mix things up from another movie but I hope not.

So characters the movie focusing on is the two brother, the little brother constantly gets treated like loser and being bullied on the school and the other is just normal. One time the little brother goes to a pizza cafe and met with the bully girlfriend, then they see a spider however he is friendly to a spider and let it go, afterward the bully came, beat him up and left him there. Feeling spite he then encounters a call from black or red phone. Which then turns him slowly into becoming a monster day by day (similar to sleepwalker monster design), he then go and kills his bully’s (he rip their heart and show it off in his two palms of hands while wearing shades) he then kills his mother and turn the house into a dark fills with dark cloud and thunder. With only his older brother left to save him or encountering him.

And that’s is all I can describe, I apologize for the horrible sentences and descriptions and thank you.