If you have gotten a new phone with a new phone number, follow the directions in this KB article: 2-Step: Re-Enrolling Phone Without Duo Device 

If you have gotten a new phone but have the same phone number, you will be able to reactivate your Duo Mobile app by:

1.  Visit the one-time passcode site located at https://smidp.uwstout.edu/otp.aspx.
   
   
2. Sign in with your username and password.
   
   
3. After clicking on the continue button you will be prompted to answer your security questions.
   
   
   
   
4. Successful answering of your security questions will provide you with a one-time passcode and at what time it will expire.
   
   
   
   
5. Make a note of that passcode, you will need it. 
   
   
6. Go to password.uwstout.edu
   
   
7. Enter your username. Click Next.
   
   
8. Enter your current password. Click Next.
   
   
9. Select Configure 2-Step Authentication.
   
   
   
   
10. At the Duo Prompt, enter the one-time passcode from Step 4 and click Login.
    
    
    
    
11. Next to your Duo device, select Device Options.
    
    
    
    
12. Click Reactivate Duo Mobile.
    
    
    
    
13. Follow the prompts on the screen then scan the QR code that is generated using the Duo Mobile app.
    
    
14. When successful, the screen will give you a green checkmark and you will be taken back to the My Settings & Devices page.