Final answer:
The correct phrase is 'put John through to,' which means the receptionist connects one person to another via phone.
Step-by-step explanation:
The correct phrase to use in the given sentence is 'c) Put John through to.' This is the common expression used when a receptionist or operator connects one phone caller with another. 'Put through' means to make a connection via phone. Neither 'put John over to' nor 'put John through by' is a standard or recognizable phrase in the English language in this context. Therefore, the receptionist was reluctant to put John through to someone else on the phone.