I’ve experimented with a couple of add-on macro lens on my iPhone, and found that they actually had too much magnification for 35mm: I couldn’t fit a whole 35mm frame in the picture and keep it in focus. The cheaper lens I tried also introduced a lot of distortion and vignetting. (I would like to make FilmLab have the ability to compensate for lens distortion, but I won’t have time to work on that before version 1.0.)
That said, FilmLab isn’t tied to any particular magnification, so if you can find a lens adapter that works for your phone and for the film size you’re capturing, there’s no reason why it shouldn’t work. I’ve been planning to try using a magnifying filter to help scan 110 film, but haven’t had a chance to try it yet.