When you are a newbie you will have the time to go and quote and I would advise you do as it is part of the learning curve.
I, like others have already said, mainly give an ESTIMATE over the phone.
You need to ask the right questions, like, where is the property, determine if a house or flat (if flat what floor, lifts or stairs only), size of room, do they know the fibre (some do, most dont), why are they having the carpet cleaned (generally dirty or stains), and other questions as appropriate.
I do emphasise prices over the telephone are an ESTIMATE, and may change on arrival and inspection.
Very, very rare do I have to adjust the estimate cause of the info received being good.
If the client wants a lot of carpets cleaned then I would prefer to go and quote, and their is more chance of closing the deal if you are there.