If there is an existing marriage contract, signed by the witnesses then an existing phone [not phony] marriage should continue and is fine. However, every modern society has institutions to stop abuse and put order into society, so these have to be used for marriages. Boys and girls listening that marriage is a personal issue between them may be led astray and ‘free for all’ ensues. Hence the need for proper witnesses [observer, spectator, onlooker, eyewitness, these mean something!] with a signed marriage contract, which is then registered with the appropriate agency.
Any irregularities in this process could result in either of the parties losing their rights, which is usually the woman.
Witnesses should be there to make sure everything is above board; one witness in America, the other in China, does not really mean we have advanced much in the last 1400 years.