Al-jawab billahi at-taufeeq (the answer with Allah's guidance)
Nikah on the phone is not valid. Also, it is a condition for the validity of marriage that the witnesses be present in the same place the marriage offer and acceptance takes place.
It is a prerequisite for the validity of the Nikah that there be two Muslim male witnesses or two female and one male witnesses. (Al-Hidayah)
Allah Ta'ala says, "And get two witnesses out of your own men (Muslim). And if there are not two men (available), then a man and two women, such as you agree for witnesses, so that if one of them (two women) errs, the other can remind her."
Additionally, non Muslims cannot be a witness.
Please refer to: http://www.cislamonline.com/fatwa_display.php?t=1031
And Only Allah Ta'ala Knows Best.