I'm not aware of any EU project to make a smartphone literally mandatory (instead of just convenient). If they do, I'll buy a separate smartphone just to hold my ID.
The EU digital id, ncluding the age verification part is (unless they fixed it already) limited to hardware attested, non-rooted, not-unlocked androids and apples for now. If you want to jerk off to porn, you're basically mandated to buy an american device (well, you will be, unless they fix it).