我相信用英文怎么说书面

"In writing" 或 "in written form" 是表示书面的英语短语。

来源：这个短语源于英语中 write 的动词形式。

例句：

Please submit your proposal in writing. (请以书面形式提交您的建议书。)
The instructions are clear in written form, but they're difficult to understand when spoken. (说明书在书面形式中很清楚，但在口头上很难理解。)