Thanks for posting in the Community, linkcommercialpr.
If you're accessing your account via the QuickBooks Online mobile app, the Bill option is not yet available through the mobile app version. You'll have to use a web browser like Google Chrome or Safari on your device or on a computer/laptop to access the bills under projects section.
To learn more about QuickBooks Online mobile app and Projects, you can check these articles:
Please let me know if you still have concern while using the app. I'm here to help you.