Retain country code in phone initialization

[aduth]

🎫 Ticket

Related to ongoing reCAPTCHA efforts, e.g. LG-8771

🛠 Summary of changes

This pull request aims to resolve an issue where the selected country associated with an entered phone number would not be preserved if the submission yielded errors, such as when trying to add a phone number already associated with an account.

This would prove problematic for reCAPTCHA efforts, where the phone number submission relies on the selected country to determine whether an exemption would apply.

📜 Testing Plan

1. Sign in
2. Click "Add a phone number"
3. Enter a phone number already associated with the account
4. Click "Continue"

Before: Country flag in phone input would show as grey box.
After: Selected country is maintained.

👀 Screenshots

Before	After