Myungsoo awoke suddenly with his heart beating and his pulse racing.

Spotting his phone on the bedside table, he snatched it to see whether it was causing the sound or not, only to find that it was.

There was a soft sniffle on the other side, "M-Myung..."

---

basically, whenever someone is about to talk or has finished talking, the format should be like this:

"asdasdasd? asdasd," he said.

you need a comma, not a period, and the letter after it should be lowercase unless the word is "I" or a proper noun.

---

Myungsoo sat up in his bed and his silky sheets slithered to the ground.

.... he wasted no time...

... as fire did when fed coal.

... and Hyeneul wept in lament.

... was an answer for him.

...until she cried all her sorrows out.

... his heart would shatter a bit more.

honestly, that's all! your story was great :))