A small voice called from within.

請教一下為何這句話from和within兩個介詞為何能靠在一塊。

A small voice called from within.

最簡單的理解是，每一個介詞后分別省略了各自的地址賓語。補充完整可以是：

A small voice called from somewhere within the house.

在實質運用中，因為常常缺少賓語，有詞典直接把 within 列為地址副詞。