Is the wife considered divorced and a divorce initiated if she is given the phone after the husband said: "I swear by divorce that you will not touch your phone again"?

What you uttered falls under the category of conditional divorce, and its ruling depends on your intention. If you intended to prevent her from taking the phone at a specific time or for that particular instance only, then her taking it afterwards does not affect anything. However, if you intended to prevent her from taking it absolutely, then by her taking it, the oath is broken.