Prepositional phrases are a group of words containing preposition which lacks either a verb or a subject. Such phrases always have two basic parts: object and preposition. Prepositions are mostly followed by objects. 

Using option A will justify all the above rules. 'Instead of' is the preposition and 'pancakes' is the object. Hence, 'instead of pancakes' becomes the prepositional phrase. 

Options B and C are not making prepositional phrases with 'pancakes' 

Thus, option A is the correct answer.