Adding phone number for log in?

Yup, what Adam said for sure. That being said, someone else asked the same question the other day, and I pointed them to the following thread (which is exactly what they needed). There are a number of other posts on this topic, too, which is why Johnny suggested you search the forum.

The bottom line is that if you want someone to be able to sign in with a phone number, you need to turn that phone number into an email address on the back end, and there will still need to be a password.