There are two options to request clients to provide their phone number.
1. You can create a new service or a meeting that will take place over the phone. You can require that the client will provide their phone number and you will call to at the time of the appointment.
Edit the Services Settings, select You will call the client under Meeting type selection. Click here to learn more on how to set up your service menu.
2. Enable the Phone Number field in the Client Card Settings. Click here to learn more about how to set up the Client Card.