Previous user phone number pre-populated on appointment confirmation form

I am very close to launching the site that I integrated Appointments+ with. I was testing by logging in as different test users and making and/or canceling appointments. During my testing I noticed something. If I log in as one user and schedule an appointment, the phone number I previously entered is pre-populated on the appointment confirmation form. However, after logging out and logging in as a different user, when I go to schedule an appointment, the same phone number as the previous user is also pre-populated in the phone number field on the appointment confirmation form.

Why is this and how can we fix that?