How do I successfully change the verification phone number if it is no longer in use?

@info1377  Well, if you have a Delorean handy...

Jokes aside, if you don't have the original phone number available, your options are fairly limited.

Which is to say, either contrive to get a phone with that phone number, or set aside an entire day to play telephone tag with QuickBooks' customer support.

I agree with, @FishingForAnswers, @info1377. 

Since logging in to your Intuit account will require you to enter a verification code, and the number you linked to it is inactive, I recommend contacting them. That way, our Customer Care Team can pull up your account privately and assess you for changing your phone number on record. 

Here's how:

1. Sign in to your QuickBooks Online account.
2. Click the Help button.
3. In the QuickBooks Assistance chat box, select Talk to a Human or tap the Contact Us button at the bottom.
4. Then, type in your reason for contacting us in the What can we help you with? Box and click Continue.
5. From there, choose a way to connect with us: Chat with us, get a Callback, or call our support line directly by getting our Phone number.

Additionally, refer to this article for other options when contacting them. You can also scroll down to the bottom to see their phone number, support schedule, and hours to contact them at the time of your convenience: QuickBooks Online Support.

You can also go over to this article to keep your billing information updated and see what you can do more to manage it: Manage billing, payment, and subscription info in QuickBooks Online. 

I'll keep this thread open if you have additional questions about managing your QuickBooks company file. The Community is available 24/7 to help you. Stay safe!