Does an expiatory oath for divorce become binding upon me after I swore not to speak to my sister until I reached Egypt, entered the house, and she apologized, then I spoke to her during my trip when she answered my mother's phone call?

You have divorced your wife via a phone call to your sister, according to the prevalent opinion (mufta bihi) among us. If this divorce does not complete three divorces, you may take her back before her iddah (waiting period) expires. However, according to the view of Shaykh al-Islam Ibn Taymiyyah, if you did not intend divorce by your oath, then your divorce has not occurred, but you owe an expiation for an oath (kaffarat yamin). One should be cautious of swearing by divorce, as it is among the oaths of the dissolute.