[User Settings] Disable phone number field if user can't edit

Same intentions as this PR (https://github.com/hackclub/hcb/pull/11895). However, disabling the phone number field is a bit more complicated bc it's a React component.

<img width="444" height="126" alt="Image" src="https://github.com/user-attachments/assets/b13441e1-16f2-44b4-a593-5081104f3dc9" />