Asalaamualaykum
The Ulema have different opinions on the issue. Some allow it, Some don't.
I have suspect most the Ulema in most countries will not risk the measure as we are in times of great Fitn.
Example: In UK certain musjids now only make a Nikah if the civil court marriage is signed first. The reason is because they have been caught out with issues of purposeful deceit of disinformation regarding the actual partner. The civil court signing already ensures that The Girl is who she says she is and the Boy is who he says he is.
In South Africa lately - a lady had been marrying men multiple times and running off with their Mehr. The examples go on and on for eternity regarding the Haraam and Fitn of people.
The Ulema rejecting phone call Nikahs this are not acting out of whims but rather taking the safest approach to ensure the Nikah is not a fraud.