you would need to edit the the spry initialization line to use a custom phone format and pattern:
for example:
var Appointment_request_group_Phone_Spry = new Spry.Widget.ValidationTextField("Appointment_request_group_Phone_Spry", "phone_number", {format:"phone_custom", validateOn:["blur"], pattern:"00000000000"});
you would also need to edit the client validation to not reformat the phone number,
Give a link to your form, Iand I will be able to give more specific instructions.