An Authenticator app, such as Authy or Google Authenticator, is a free app available through the App store or Google Play store that enhances account security. Put simply, these apps generate temporary codes that allow you to protect against password theft. The codes that these Authenticator apps provide you are temporary codes that are only available through your device.
Authenticator apps are not reliant upon having your phone number. When using this type of 2FA, your account will be secure even if your phone number and password are compromised. In other words, rather than Voyager sending you an SMS verification code to complete 2FA, your authenticator app generates these temporary codes for you, which you will use to sign in to your Voyager account.