If you leave smartphone unsplit, google doesn't try to translate it:
There is no standardisation among the French speaking countries to name a smartphone and even less a mobile phone. The latter can be portable, mobile, GSM, Natel, cellulaire…
If your academic paper is written in a French (of France) context, you might simply keep smartphone. This is the most common term. Smart has already been adopted since more than one century in French and the -phone suffix is standard French. If you really want to stick with the formal recommendations, that should be ordiphone or terminal de poche but the former is very rarely used and the latter is imprecise (a terminal de poche might not be a phone at all.)
If you are writing in a Canadian context, you should follow the local recommendations and use téléphone intelligent.
In an unspecified context, you might use whatever term. French Canadians will definitely understand what you mean with smartphone and téléphone intelligent while uncommon here is perfectly understandable.
Whatever your choice, you might add a footnote explaining what you mean, for example like this:
Cette étude s'intéresse à la durée d'utilisation des smartphones1 en fonction de l'age.
In any case, don't use malin in an academic paper. Malin might be used in advertising or for fun, but might not match smartphone at all, see for example that page which call Un téléphone malin à un prix attractif ! a wireless home phone without any functionality expected from a smartphone.
Today's Journal officiel 2 contains an updated list of some official telecom sector French terms with their English equivalent.
The previously recommended terminal de poche has been dropped and now a smartphone is expected to be named mobile multifonction or simply mobile. I find these new recommendations much better than the older one.
1 ex: de type iPhone ou téléphone sous Android.
2 The Journal officiel is a daily government publication containing new laws, decrees and various other legal and informative texts.