I'm trying to catch Mary, please.

我想与Mary联络。

May I speak to Miss Tan, please?

可以请谭小姐听电话吗？

Shall I tell him you called?

我告诉他你来过电话，好吗？

Have you been here to see Dr. Tyler before?

你曾来过泰勒医务所看过医生吗？

I'm calling to know if it would be at all possible to cancel our reservation.

我打电话想知道我们的预约是否有可能取消。

Why not?

为什么不能？