If your notification said the Guardian "has stopped guarding your wallet" it means they no longer want to be your Guardian. We'd advise you to replace them with another Guardian.
If your notification said the Guardian "will be removed in <time>", and you didn't request the removal, you have 24 hours to review the change and prevent it, if you want.
To cancel the removal, you should lock your wallet. This will prevent the change from taking place. You can then recover your wallet on a new phone.
If the unrequested Guardian removal occurred while you did not have access to your phone, you should lock your wallet and recover it on a new phone.