In the July released you will find a good collection of new mobile workspaces. One of these is the expense management workspace. This has basically the same functionality that used to be in the expense app that was available for AX2012. The benefits of the new architecture is the setup, it is much simpler technically to get these apps live. Just published them from the mobile app admin.
In this app you can do the usual expense functions. Capture a receipt that you can reconcile later. Enter an expense line that you can then add to a report later. Submit the expense for approval and review approvals.
Here is a quick overview.
D365 July 2017 Update 8 (7.0.4565.16211)