Your cell phone email address must be a valid email-style address. Something like "4135861234@txt.att.net"

You phone number is not enough.

Every phone company is different and you need to Google them to find what works for yours and then try it yourself with a test email. The addressing format changes often.

Because of that, cell phone email addresses are deleted each summer. You must sign up every August to be on the list again (you will receive a reminder).