what type of phrase is under the staircase?

http://grammar.ccc.commnet.edu/grammar/phrases.htm#preposition

is it a prepositional phrase???

Yes!

=)

To determine the type of a phrase, we first need to understand what a phrase is. In grammar, a phrase is a group of words that work together to convey a specific meaning, but it does not have a subject and a predicate combination like a complete sentence.

The phrase "under the staircase" consists of the preposition "under" and the noun "staircase". The preposition "under" indicates the relationship of position or location between the noun "staircase" and something else.

In terms of classification, the phrase "under the staircase" is an example of a prepositional phrase. A prepositional phrase typically starts with a preposition (in this case, "under") and ends with a noun or pronoun (in this case, "staircase"). The prepositional phrase functions as an adverbial or adjectival phrase, modifying a verb, adjective, or noun by adding more information about its location or position.

So, to determine the type of the phrase "under the staircase," it is a prepositional phrase.