I don't think so.
The expression "couch potato" was coined quite a few years ago to describe a person who had a certain behavior pattern that was commonly talked about at that time: namely sitting on the couch for too long watching television, specifically television.
I'm sure you are right that the objectionable aspect of this behavior is passivity and lack of physical exercise (maybe mental exercise too), but the expression is really about television. I don't believe it has been updated in common use to include smart phones.
It isn't hard to understand what you mean if you mention the term "couch potato" when you are talking about smart phone addicts, but you should make it clear by indicating explicitly that you mean video games or social media, etc.
I was becoming such an i-phone couch potato that I felt I had to join
That guy is so boring; he's a real video game couch potato.