The elevator does not give a floor number but a referring expression for it. The elevator is able to resolve the referring expression and realise that The top floor is the fifth floor.
System:
Which floor do you want?
User:
Phonetics
System:
Do you want the 4th or the 5th floor?
User:
The fifth floor, please.
The same here. The system resolves Phonetics to be referring to either the fourth or the fifth floor. Being aware of the ambiguity, it requests a clarification.