Hi
Welcome to the Microsoft community.
Because you have changed your phone number, the only thing you can do is to retrieve your account number and check whether you can retrieve the bit lock key. You can try the following link to recover the form.
Help with the Microsoft account recovery form
BitLocker recovery guide (Windows 10) - Windows security | Microsoft Docs
Finding your BitLocker recovery key in Windows (microsoft.com)
You are welcome to reply to this topic, and I sincerely thank you for your support of Microsoft products and services.
Best regards
Derrick Qian | Microsoft Community Support Specialist
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