Pros and cons of registration on a website with phone number instead of email address

I’m developing a small website for a local sports club. Currently I’ve set it up with a standard email registration system – i.e. user enters username + email adress + confirmed password; server returns an email with registration link; user clicks on link to complete registration.
But since nearly all members of the club already communicate via WhatsApp, would using phone numbers be better? Passwords would still be required, since the site will be accessed via browsers rather than a phone app like WhatsApp. An advantage of using phone numbers is that the server could be asked to send out texts to users if an event is cancelled at the last minute – more likely to be seen than an email. Of course , registration could involve both email and phone but users may be aware of identity theft and not like that.
There’s clearly a small cost implication, since a text message costs a bit when sent from a server, whereas an email does not. But are there any other issues to take into account?