The Dvorak simplified keyboard is optimised for low finger travel distance, leading to faster typing and less wrist pain compared to the Qwerty layout. On a smartphone, most people effectively only type with one finger, either by touching the letters or by swipe typing. Dvorak may therefore not be optimal for smartphone keyboards; see also this question on a swipe specific keyboard.
However, Dvorak also designed right-handed or left-handed single-hand keyboard layouts, such as this right-handed layout:
I would suspect that a single-handed keyboard layout is a better approximation of smartphone typing than a dual-handed keyboard layout. Has there been any research comparing the hand travel distance when "typing" (either by touching keys or by swiping) on a small touchscreen (such as a smartphone) using either Qwerty, normal Dvorak, single-handed Dvorak, or even a totally new layout optimised for smartphone usage?
Closely related: How to improve the smartphone keyboard layout?