I imagine you'll be able to write apps in Qt/QML[1], which already provides a UI optimised for a phone[2]. [1] Available in Debian, and therefore by extension,

I imagine you'll be able to write apps in Qt/QML[1], which already provides a UI optimised for a phone[2]. [1] Available in Debian, and therefore by extension, PureOS [2] SailfishOS, the other mobile Linux OS, uses Qt/QML for its apps