Is a marriage contracted over the phone, without a guardian (wali), witnesses, or public announcement, with the words "I marry myself to you" and "I accept your marriage," considered valid in the Hanafi school of thought, and does it necessitate a divorce from the current husband?

What occurred between the woman and the young man was a form of jest; it does not constitute a valid marriage according to Abu Hanifa or any other scholar. Marriage has conditions and pillars without which it is not valid. The mere utterance of acceptance (qabul) and proposal (ijab) without a guardian (wali), witnesses (shuhud), or dowry (sadaq) has not been considered a valid marriage by any scholar. There is no need for divorce or annulment. The woman should not preoccupy herself with this matter as long as she has repented to Allah Almighty from this relationship.