在书桌上用英语可以说是 "on the desk"。这个短语来自英语中的介词 "on" 和名词 "desk"。例句如下：

Please put your books on the desk.

The pen is on the desk. Can you please pass it to me?

I left my phone on the desk. Can you please grab it for me?

在英语中，"on" 通常用来表示物体的位置，表示物体的支撑物或某物所在的表面。例如：

The cat is on the table.

The picture is on the wall.

The lamp is on the nightstand.

而 "desk" 是指书桌，是一个平面放置物品的家具。例如：

She sat at her desk and started to work.

He cleared his desk before leaving the office.

The desk was cluttered with papers and books.