Uphold uses a Time-based One-Time Password (TOTP) algorithm for Two-Factor Authentication. The TOTP algorithm is an extension of the HMAC-based One-Time Password algorithm (HOTP), generating a one-time password by taking uniqueness from the current time.
TOTP token services rely on a physical device, rather than a phone number. In addition to increased security, TOTP provides benefits that include working without an internet connection and compatibility with a range of applications like Google Authenticator, Microsoft Authenticator, Authy, and password managers like 1Password and LastPass.
Read more about the supported Two-Factor Authentication apps for TOTP.