Hi Paul Willems - AP2PM, I can imagine how frustrating this must feel being locked out of your own device and account because of an outdated phone number especially when you need that BitLocker key urgently.
To fix this issue update your Microsoft account security info by signing in and adding your correct phone number then removing the old one then wait the mandatory 30days verification period before using the new number while in the meantime checking for your BitLocker recovery key on a USB drive printed copy local file or through your organizations Azure AD or Lenovo support and if possible use a trusted device or contact Microsoft Support for identity verification.
Do you currently have access to any backup recovery options such as a USB drive or printed BitLocker key or another trusted device linked to your Microsoft account?
Best regards
Lucky Charm