Are my customers' phone numbers anonymized?

It depends on what you enable, and it's your choice: by default, numbers stay readable in your dashboard because a plumber has to be able to call Mr. Tremblay back — anonymization by default would make the service unusable. Pseudonymization, however, is available for read-only roles and exports shared with an accountant or partner: numbers appear masked there, derived stably so duplicate tracking still works. After the retention period you choose, inactive numbers are hashed automatically. All of it complies with GDPR: declared purpose, minimization, limited duration.