[zinekeller]

To be fair, it really depends on the region you're operating. Some regions (like most places in Asia) use this as the primary identifier (instead of email), so despite the very obvious security flaws you might be simply be forced to offer it.

[jhugo]

Right, by this point the global norm is to rarely, if ever, use email (or a computer larger than a smartphone) unless you work in an office (and in some places not even then). The phone number is the primary identifier for mass-market apps in most countries.