Do I need to provide my mobile phone number to set up MFA?


It depends on the authenticator app you choose to use for Multi-Factor Authentication.  Both the Google Authenticator and RapidIdentity apps that run on your mobile device use a time-based one-time password (TOTP or OTP) algorithm to compute a valid 6-digit code (it is not texted to your phone).  So while these applications RUN on your phone, you are not sharing the number with anyone nor being changed any fees.  However, Authy (one of the alternate authentication apps that runs on your desktop), does requires you to enter your cell number when installing and registering the application with the vendor.