How do I change the registered phone number of the admin ID?

I'll point you in the right direction for support with your query about changing the registered mobile number in QuickBooks Online (QBO), @Codelattice_123.

I suggest you contact our Technical Support team for this specific issue. They can pull up your account within a secure environment and assist with this concern. Open this article for the steps: QuickBooks Online Support. 

Keep this article for future reference as well: Reset your password or recover your user ID for QuickBooks Online. As the article states, it includes the steps on how you can resolve user ID or password issues.

Let me know in the comments below if you have other questions about your QBO account. I'll get back to you as soon as I can. Enjoy the rest of the day!