If you have a TRO-capable iPhone/iPad app that syncs with your main task list, install it using the publisher’s instructions.
Mobile apps don’t usually do everything. That may be OK—when you work on the road, it’s usually just collecting and working off lists. However, look for an app that supports most or all of the important TRO lists for mobile devices. Configure the app to match the TRO setup of your online or desktop task list as closely as possible. Consider fields, layout, sorting, fields, and default views.