Have you neglected to ask (or continue to ask) the kinds of questions that enable you to woo, win and wow them….um, in other words, get and retain your clients' business?
Why are you asking if they can meet with you on Tuesday morning or Wednesday afternoon (pulling out that age-old "alternative choice" close) rather than taking a few moments for them to reveal their situation, wants and needs? Do you think that you'll "lose the appointment" if you "waste" too much time on the telephone? In my 24 years of experience, this has rarely been the case. Rather, prospects appreciate the consultative approach and provide the kind of input that makes for a qualified and more beneficial in-person meeting.
Always have a slew of questions in your sales toolbox and use them appropriately. Ask insightful questions whether speaking with a new prospect or an existing client (after all, things change and you must be on top of changes in the client's circumstances lest you get left behind).
Here's a good rule: Make sure to learn one new piece of information whenever you are having a conversation with a prospect or client, whether it be in-person or on the phone. For existing clients you may simply say "I want to make sure that I'm entirely up to date on your account so that I may be a better resource for you. Can you tell me ___________?" And then ask your questions.