Nikah on phone

so if a wakeel appointed by gal is not physically present inf ront of groom at the time of nikah then nikah is not valid? if nikah is not valid in this scenario then is it still valid for paper purposes? if not valid for paper purposes then y do ppl do it if it’s not valid in islam/for paper purposes w/o physical presence of wakeel in front of groom at time of nikah?