In my industry, as important it is to quickly respond to both clients and prospects, it's also extremely important to show respect by NOT answering my phone when with a client or prospect.
To work this delicate balance, I do 4 things:
1. I turn my phone to "do not disturb" when in a face to face appointment.
2. I have a message on my voicemail indicating I will call back as soon as I can.
3. If I'm between houses, I will send a quick text letting them know I'll be back in touch soon.
4. I set the expectation up front that if I don't answer, there is a reason, and be assured I will call back as soon as possible.
This helps me manage my time to best serve my clients and prospects, while demonstrating that I value the time they have set aside for me.