We had a sudden bombardment of student accounts end up being called out for suspicious login attempts this week as they attempted to login to on site chromebooks. All of them had a phone number attached to their accounts that caused MFA confirmations requirements. Staff had to go into each account and remove the associated phone number to allow the accounts in question to login again.
I feel it is worth noting that we are a phone free school, and that it is possible that some parents are logged in to their student's accounts on the parent's phones.
Edit: I want to clarify that the issue is two fold: first is that phone numbers are being associated with accounts without users being informed, as long as they are added to an android phone.
Second was the suspicious login messaging, which CAN be seen with a sudden burst of requests or logins from an IP or gateway apparently (we normally see this behavior at the start of a new school year) but could also be triggered when an account is logged in on a device and another login attempt occurs where the connection traces to a different geolocation.
From Android Authority:
https://www.androidauthority.com/google-auto-phone-number-verification-android-3723117/
Copy/pasted select sections:
PSA: Google is silently linking your phone number across all signed-in accounts
Android’s phone number verification setting is opt-out, and links your number across every Google account on your device.
TL;DR
Google now automatically verifies and attaches your phone number to every Google account signed in on your Android device without explicit prompts.
Google updated its documentation between August and October 2025 to reflect this opt-out behavior, which links numbers across secondary, work, and alt profiles.
Users can turn off “Verify phone numbers automatically” in their Android device’s Google settings page, but previously linked numbers must be manually removed from each Google account’s Personal Info page.
Note that turning off the phone number verification toggle only prevents future linking. If Google has already attached your number across secondary accounts, you will need to open your Google Account Personal Info page, head to Contact info > Phone, and manually remove the number from each profile where it doesn’t belong.
