Detlef, I'd probably tackle this by using "Phone" as the context, and then putting something like "#10" in the action title. You'll still look in the phone context for all your phone-related actions, but you can also find all the 10-minutes-or-less actions by entering the 'hashtag' for that category into the search field. Does that work for your purposes?
(From the credit-where-it's-due department:
http://hashtags.org/)