Answer:
Step-by-step explanation:
The mayonnaise in the tuna salad was spoiled, and it made me sick.
The phase in bold letters was the prepositional phrase.
It modifies was spoiled (where is the mayonnaise. The trick is not to think that it modifies mayonnaise. (what kind of mayonnaise is in the tuna salad?)
the phrase tells where it is, not what kind it is.