在您的MFA设置中的从Active Directory导入"下，点击已启用" 所有用户"旁边的复选框并选中更新现有用户"复选框.当您添加任何新用户时，现有用户也将 即使未使用电话号码导入也已启用MFA.

请从我的MFA服务器实验室中查看以下屏幕截图.

In your MFA settings under "Import From Active Directory" hit the "Enabled" checkbox next to "All Users" and also select the checkbox "Update Existing Users." When you add any new user the existing users will also have MFA enabled even if they were not imported with phone numbers. 

See the below screenshot from my MFA Server lab.