"以文字损害名誉" can be translated into English as "defaming someone's reputation through written words" or more concisely as "defamation by written means" or "written defamation".
Here are some examples of how this phrase might be used in a sentence:
He was accused of defaming someone's reputation through written words in his article.
（他因在文章中以文字损害他人名誉而被起诉。）
The court found him guilty of written defamation.
（法院判定他犯有书面诽谤罪。）