To change the phone number where you get your security code, you need to update it in your login.gov account. Go to login.gov and read their help page:
How do I change the phone number I use to sign in?
Will updating my phone number in my login.gov account also update the phone number in my USAJOBS profile?
No. The phone number you have in your USAJOBS profile is separate from the phone number you have in your login.gov account. If you want to change the phone number in your USAJOBS profile, you need to go to your profile and edit your contact information.