assalam alaikum

is nikah permissible over the phone

jazakallah
باسمه تعالى
One of the conditions for the validity of Nikaah is the presence of Aaqid and Aaqidah-bridegroom and bride or his/her Wakeel-proxy at the place of Nikaah where the witnesses listen to the Eijaab-proposal and Qubool-acceptance of the couple. This condition does not meet in the case of Nikaah over the phone. Therefore, Nikaah over the phone is not permissible.

However, if one is far away and cannot be present at the place of Nikaah, one can appoint someone as Wakeel-representative to propose or accept the conduct of Nikaah on one’s behalf.
والله اعلم