What are the prepositional phrases in "The Fly"?

A prepositional phrase begins with a preposition and is followed by an article (a, an, the) and a noun or just a noun (without an article). Prepositions often give a location, such as "on," "under," "over," "around," "for," "from," and "by." For example, "the fly is on the shelf" or "The fly flew above my head." They also can tell who something is for or from: "the flyswatter is for the fly" or "the bug-spray is from the market."
“Of” is also a lesser-known preposition that shows belonging or relation. For example, “I am the of the house of Fly,” meaning “I belong to the important house of Fly.” Or “I am of royal fly blood,” meaning “I am important because I am related to royal flies.”
The word "like" is also a preposition, although usually a lesser-known one. It makes a comparison. “On a hot day, families swarm around the ice cream shop like flies.”
In William Blake’s poem, the speaker addresses the fly (a device called apostrophe) in order to contemplate his own frailty:

Little fly,Thy summer’s playMy thoughtless handHas brushed away.
Am not IA fly like thee?Or art not thouA man like me?
For I danceAnd drink and sing,Till some blind handShall brush my wing.
If thought is lifeAnd strength and breath,And the wantOf thought is death,
Then am IA happy fly,If I live,Or if I die.

In the second stanza, there are two comparisons made with prepositional phrases. “Like thee” is one prepositional phrase, where “like” is the preposition and “thee” is the object of the preposition. The second is similar: “like me.” The speaker simply reverses the question in effort to say, “I am just like you, Fly, and you are just like me.” The preposition is used to set up a more detailed comparison of how they are alike. Sadly, the ways they are alike are kind of depressing: they could both be swatted dead by the hand of providence at any moment—they have no control over their mortality. The second comparison the speaker makes to the fly is that if they both suddenly die, neither will know they are dead because they won't be able to think. So the thought of being dead won’t nag at them like a gnat on a hot summer’s day.
In the fourth stanza, where the second comparison is made, another prepositional phrase appears: “Of thought.” This prepositional phrase is part of the subject of the clause. The entire clause (or complete idea with a subject and verb) is “And the want of thought is death.” This sentence is saying that the absence of the ability to think is equal to death, or in other words, when the mind stops thinking, one must be dead. Without the preposition “of thought,” this idea would not be clearly understood by the reader. It would say, "And the want is death," which entirely changes the meaning. So, as you see, prepositional phrases add important detail to poems, stories, and essays, and detail is powerful because it can help you to more clearly be understood.