A prepositional phrase is any grouping of words that describes where, how, when, something is done or which one has done an action. "The ball was found under the bed." is an example of a sentence with a prepositional phrase that describes where something is.
Call as a verb:I will call you tomorrow and let you know what time I will be coming.He called her name, but she couldn't hear him.Call as a noun:Lack of phone service prevents me from placing a call.Telemarketing calls are really annoying.Call is not a pronoun, adjective, adverb, or preposition.