What's a phrase? According to Crews, a phrase is a 'cluster of words functioning as a single part of speech and lacking a subject-predicate combination.' A phrase is a bunch of words without a main verb.
A. Prepositional phrase - The zebra ran to the river.
Prepositional phrases function as adverbs or adjectives. In the example above, the propositional phrase is an adverb because it indicates where zebra ran (adverbs indicate where, when, why, or how). In the following example, the prepositional phrase is an adjective because it modifies a noun:
The zebra in the river was young.
B. Infinitive phrase - The lion's attack caused the zebra to run toward the river.
C. Participial phrase - Running toward the river, the zebra escaped.
D. Gerund phrase - Attacking zebras was seldom successful.
By recognizing clauses, phrases, and other elements, you will be better able to modify your sentences and therefore increase the your writing's effectiveness. Note that these phrases often end in a noun, which is called the object of the phrase.