Yes, your observation is right. The Billable option is currently not in the QBO mobile app. For now, please utilize the online version when you enter billable expenses.
I’d encourage you to vote on the existing feedback about this. Here’s the link: http://feedback.qbo.intuit.com/forums/168199-quickbooks-online-feature-requests/suggestions/6163725.
Resolution for 'Billable option issue: 'how do i enter a billable bill on my iphone? Looks like i can only do online.' available: Yes.
The Billable option issue or error code is a known issue in Quickbooks Online (QBO) and/or Quickbooks. Support for this issue is available either by self-service or paid support options. Experts are available to resolve your Quickbooks issue to ensure minimal downtime and continue running your business. First try to resolve the Billable option issue yourself by looking for a resolution described in the article. If it is a complex Billable option issue or you are unable to solve the issue, you may contact us by clicking here or by using other Billable option support options.
For more information about resolving issues related to Billable option in Quickbooks/QBO or to get support for the issue 'how do i enter a billable bill on my iphone? Looks like i can only do online.', click the link below: