Fill in the blank with the suitable Adverb Phrase from the given alternatives.

A soldier is trained never to fight ________.

in a cowardly manner

The suitable adverb phrase to fill in the blank is: in a cowardly manner.

Here's why:

• "In a coward manner" is grammatically incorrect as "coward" is a noun, not an adverb.
• "Like a cowardly" is not complete and lacks a preposition.
• "Cowardly" alone works as an adverb, but it's more impactful and descriptive to use the full phrase "in a cowardly manner" to emphasize the negative connotation of the soldier's behavior.