The fact they are using this phrase implies they may scan or read it for other purposes, for example I'm sure they use it to train their neural networks. What else? I don't exactly know and that's a problem.
To be argumentative, though, I would wager a lot of money that you don't know what _exactly_ your SMS messages are being scanned for either.
Precisely, this is why I try to limit my use of services that require my phone number for any reason, and sms messaging in general.
Spam filtering.