Islamic Muftis and Scholar has clearly said that Nikkah don,t takes place on Phone because on Phone you don,t know who is person on other side and Voice can also be changed on Phone. In Islam Nikkah takes place face to face in presence of eyewitnesses.
So the conclusion is that Nikkah of Shoaib Malik and Ayesha Siddiqi has not taken place. Mufti Azam Hyderabad Deccan that is city of Ayesha Sidiqqi has also the same opinion. Now i come to another matter that is even if a man has done one marriage he is allowed to do second marriage without taking permission from first wife. The condition for doing more than one marriage told in Quran is doing Justice between wives. So islamically Nikkah of Shoaib Malik has not taken place with Ayesha Sidiqqi and he is allowed to do marriage with Sania Mirza.