Your password manager asks you to verify the new phone
Your password manager is doing exactly what it should: distrusting a device it's never seen before. The problem is when the way you prove it's really you lived only on the phone you're leaving behind.
In short: a dedicated manager (Bitwarden, 1Password, Proton Pass…) asks for a second factor or your emergency kit when you sign in from a new phone. A browser's built-in manager asks for your Google or Apple account verification instead. In both cases, if that second factor lived only on the old phone, you've just locked yourself out of your own manager.
What happens
Installing your password manager on a new phone, besides the master password (if you use a dedicated one), usually asks for a second step: a code from an authenticator app, a confirmation email, or approving access from another device where you already had a session. If you use your browser's built-in manager — Google Password Manager in Chrome, or iCloud Keychain in Safari — the same thing happens, but through your Google account or Apple ID: the browser syncs your passwords to that account, and signing into that account from a new device triggers its own verification.
This is where the most common trap shows up: if your 2FA for the manager lives inside an authenticator app that, in turn, only exists on the phone you're switching away from, you've built yourself a circular dependency. The manager asks for the authenticator, the authenticator lived on the old phone, and the old phone is exactly what you no longer have handy.
Why it happens
Because a password manager holds, literally, the keys to almost everything else: it's reasonable that it protects itself more than any ordinary account. The price of that protection is that, if its own second factor depends only on the device you're replacing, the lock that protects you is the same one locking you out.
This isn't a flaw in the manager: it's the consequence of it doing its job well. A manager that let anyone in from any new device without question would be far less useful as a vault. The weak point isn't that it asks for verification, it's where you decided to keep that verification.
Who it hits hardest
People who set up their manager's 2FA with an authenticator app with no backup, thinking that made it "more secure" than email. And people who use the browser's manager (Chrome or Safari) and assume that because "it's all in the cloud already," there's nothing to check: the cloud still asks to verify who you are.
It also hits people who share a manager with a partner or family (a family plan on a dedicated manager, or several Google accounts on the same browser): each person has their own second factor, and switching phones for one of them doesn't fix it for the others.
What to check before you switch
- Do you know what second factor your manager will ask for when you sign in from the new phone?
- Does that second factor live only on the phone you're leaving, or does it have a backup somewhere else?
- Do you have your manager's recovery code or emergency kit located (if you use a dedicated one)?
- If you use the browser's manager, is the Google or Apple account that holds it protected by something other than just this phone?
If it already happened to you
If you can no longer get into your manager because the second factor stayed on the old phone, each manager has its own account-recovery path (a saved recovery code, identity verification, or contacting their support); there's no shortcut common to all of them. While you sort it out, any account whose password you only had there is out of reach unless you remember that password from memory or have it saved somewhere else you trust.
Official sources: Google: Google Password Manager