Phrases which are important to the story and help move it forward are many in this short story, so I will select just a few and comment upon each.
1) Firstly, the opening sentence is key in setting up the central irony of the story, as it refers to the "heart trouble" that Mrs. Mallard has. This becomes crucial at the end of the story.
2) What is most interesting about the story is the way that when Mrs. Mallard locks herself away in her room and looks out of the window, what she sees is representative not of death but of new life:
She could see in the open square before her house the tops of trees that were all aquiver with the new spring life. The deliciouis breath of rain was in the air.
This is the first indication that Mrs. Mallard views the death of her husband not as a tragedy, but as something that bestows the gift of life to her.
3) What then becomes important is her own realisation of her state as a widow, as she says to herself, "Free, free, free!" The accompanying physical feeling of release reinforces this speech.
4) The reference then to her own feelings of freedom and how marriage is described as having a "powerful will bending hers" captures the theme of marriage as something negative in the short story.
5) Finally, and most tragically, the short story ends with the shock of her husband's reappearance, and the dramatic irony that she died apparently of "joy that kills" because of her heart disease, whereas the reader knows it was not joy at all.