Not sure why two step authorization hasnt been built into the mobile app. The solution of disabling the protection, logging on your phone, then reenabling it is backwards and time consuming.
Update 4/5/16: Todays update still doesnt have two step authorization support. Refuse to disable this just to log into the app
Update 4/19/16: No 2 step authorization today either
Update 4/26/26: I had put in a request to support asking for the timeline for implementing 2SA to the app. They suggested putting in a feature request on the Forum, which there is already one. If you find the app useless because of this flaw, up vote the "2SA - Touch App login that supports two step authentication" in the community forum
i.mcdaniel about Xero Accounting for business