You may be allowed to disable MFA on your My Preferences page via Actions menu > Disable MFA. If MFA is required for your user role by your site administrators, you will not be able to disable it.
Site administrators can disable MFA, or change a user's MFA Method, by editing those fields on the user record. Those fields are typically not shown, or not editable, on the user profile, but are on an auxiliary form restricted to only Administrators.
I Lost/Replaced My Phone/Device (Re-Enabling MFA)
A site administrator will need to disable MFA for your account. When you next login, you can enable MFA again, or if it is required for your user role, you will be forced to enable MFA again.
Enabling MFA for a Site (Site Administrators)
Visit the Admin > Site Settings page and look in the Authentication section.
Requiring MFA (Site Administrators)
Administrators can require MFA per user role on the Admin > Site Settings page.
Note well the note shown below the list of user roles: "Users whose role has the API Access permission will not be required to implement MFA."
Also note well that you should not select the Pro Bono Restricted Access role. It will prevent them from logging in. This role is not yet supported.
There are two fields on the System Users table that tie in with MFA. A boolean about whether MFA is enabled and which MFA mechanism in use. A sample report about all users and whether they have MFA enabled can be found in Example Reports.