At this moment (end of the year, 2017), the description for Lego Boost on the french amazon site includes the notice:
Enfin, l'application sera également disponible sur smartphones dès les vacances de fin d'année.
(translates to: Finally [it's after the list of compatible tablet Os'], the application will also be available on smartphones from the end of the year vacation.)
Has anyone read anything about this elsewhere? I'm failing to find anything on google, the LEGO site or the German or UK Amazon sites.