Sometimes I get invited to text a message to 123456. How does my phone / phone service know the real destination? I understand using an email address composed of the 10 digit phone number @ server domain.
Just ike you get cold calls on your home phone, text messages on your smart phone are the same. Robo call a series of numbers and they cross their fingers that they got a live person who just may answer.
Follow the rule, if you don’t know who the sender is, block the number and then delete it.