。
The walls are closing in.
Literal
Wall [subject-が] pressing come.
迫ってくる combines 迫る (to press/approach menacingly) with ~てくる (coming toward the speaker). The result is a vivid sense of the walls advancing — whether literal (as in a trap) or metaphorical (as in feeling trapped). ~てくる adds the crucial 'toward me' directional element.