This is the 11217th most frequent Polish word.
gruszką
"Gruszką" means "pear" in English (instrumental case).
Here, 'gruszkę' is used as the accusative case of 'gruszka', referring to the fruit.
Mam ochotę na gruszkę po obiedzie.
I feel like having a pear after lunch.
In this context, 'gruszką' refers to a colloquial term for the receiver part of an old telephone, in the instrumental case.
Czy mogę się włączyć do rozmowy swoją gruszką?
May I join the conversation with my receiver?
The word 'gruszką', here in instrumental case, refers to a lever shaped like a pear, used in machinery.