Here is a little "hack" that worked for me:
Find these lines in PhoneTexting.rpy:
if d.who == MC_Name: color "#FFF" text_align 1.0 xpos -580 else: color "#000"
Replace the xpos -580 with this:
if renpy.variant("small"): xpos -1067 # adjust this number as you see fit else: xpos -580
Now the whole code should look like this:
if d.who == MC_Name : color "#FFF" text_align 1.0 if renpy.variant("small"): xpos -1067 else: xpos -580 else: color "#000"