Prepositional phrase is a type of phrase which consists of a preposition and an object. It usually begins with the preposition and it is the main part of the phrase. The second part of the phrase is an object which is a noun or a pronoun. In a sentence, this phrase most often acts as an adverbial.
So in this case <em>from</em> is a preposition and <em>the group</em> is the object, together they form a prepositional phrase.