Unfortunately, that is correct. Following is from the PowerApps coding standards white paper:
"When you make the same PowerApps app target both phone and tablet layouts, first create one version of the app, run it through testing, and finalize it. Then convert it to the other version before you modify the layout and screens. This approach helps guarantee that your expressions, controls, variables, data sources, and so on, all have the same names. Therefore, it’s much easier to support the apps and develop them".
Of course, this approach does not make it easy to maintain the app, as any changes will need to be done to both apps. The white paper also links to a blog for instructions on how to do the above:
How to convert a PowerApp from one layout to another
