Another really scary one could be 'My phone rang at 3 am. The caller ID said it was me.' It plays on the idea of the self being something other or unknown, and calls at that time are always spooky.
One way to sentence horror stories is to build suspense gradually. Start with an ordinary setting or character and then introduce strange elements little by little. For example, you could begin by describing a normal day in a small town. Then mention a strange noise that no one can identify or a person who behaves oddly. Use vivid language to describe the uneasiness that starts to spread among the characters. This makes the readers feel on edge as they wonder what will happen next.
I think 'The clock stopped at midnight. Then I heard footsteps.' is quite scary. It gives this feeling of something ominous starting right at a spooky time.
They are concise. For example, 'The phone rang in the dead of night. It was my voice on the other end asking for help.' In just two sentences, it creates a sense of dread. They often rely on the unexpected. Like 'I found a door in my basement that wasn't there before. When I opened it, a cold hand grabbed mine.' It takes a normal situation and twists it into something terrifying.
I'll share this. I found a diary in an old attic. The last entry said 'They're coming for me tonight' and then the handwriting turned into scribbles. I started to hear scratching noises on the attic door right after reading it.
Story 1: The old house stood alone in the dark woods. Every night, a cold hand would reach out from under the floorboards. Story 2: She walked into the empty classroom. A shadow on the wall began to take the shape of a menacing figure.