Fix: Claude Phone Number Already in Use Error

To prevent spam, abuse, and automated bot registrations, Anthropic requires a valid mobile phone number during the registration process for Claude.ai. However, many users encounter the frustrating message: "This phone number is already in use."

This error occurs because Claude strictly enforces a 1:1 link between a phone number and a user account. If you attempt to verify a new email address using a phone number that is already associated with another Claude profile, the system will block the registration. Here is how to troubleshoot this issue, locate your original account, and verify your identity.

Why this error happens

There are three common scenarios that trigger this error: 1. Multiple sign-in methods: You previously logged in using "Continue with Google" or "Continue with Apple," but later tried to register with an email and password using the same phone number. 2. Recycled phone numbers: You recently acquired a new mobile phone number, and the previous owner used it to register for Claude. 3. Accidental duplicate account creation: You forgot you already created a Claude account in the past with a different email address.

Step 1: Identify your original login method

Most occurrences of this error happen because a user has multiple active email addresses or identity providers (Google, Apple, Microsoft) and forgot which one is linked to their mobile number.

1. Sign out completely from Claude.ai.
2. Go to the login screen and attempt to log in using "Continue with Google" with your primary Google account.
3. If that does not work, log out and try "Continue with Apple" (if applicable).
4. Try entering any alternative personal or work email addresses you may have used in the past.
5. Once you find the correct account, your mobile number will already be verified, and you can access the interface without registering a new profile.

Step 2: Check for VoIP or virtual number restrictions

Anthropic uses verification services that block temporary, virtual, or VoIP phone numbers (such as Google Voice, Skype, or burner app numbers).

1. If you are trying to use a virtual number, the verification database may flag it as "in use" or "invalid."
2. Ensure you are using a standard, post-paid or pre-paid mobile phone number from a major carrier.
3. Switch off Wi-Fi calling on your phone temporarily during the verification process, as this can sometimes interfere with carrier-level routing.

Step 3: De-link or delete the old account

If you have identified the old account that is holding your phone number but you prefer to use your new email address, you must manually delete the old account to free up the number.

*Note: Account deletion is permanent and wipes your history.*

1. Log into the Claude account currently holding your phone number.
2. Navigate to your profile icon in the bottom-left corner and select "Settings".
3. Select the "Account" tab.
4. Click "Delete Account" and confirm the prompt.
5. Once deleted, the linked phone number should eventually be released back into the system, allowing you to register your new email address. (Please note that release latency can vary from instantly up to 48 hours).

When to escalate

If you have a newly assigned mobile number from your carrier and have never registered for Claude yourself, the number is likely tied to a previous owner's dormant account.

Because you cannot log into the previous owner's account, you must contact Anthropic's team directly. Visit support.anthropic.com, submit a support request under "Account Verification," and explain that you have a recycled mobile number. Be prepared to provide a recent carrier bill showing your name and the phone number to verify ownership so they can manually clear the number from the inactive account database.