I searched Google, because I was wondering why texts from numbers not on my contacts weren't being filtered, turns out that only works with iMessage, which I have turned off.
It should gray that setting out if you don't use iMessage, and put a big warning by it, that it doesn't filter regular SMS.
Somebody on Reddit said they use SmartFilter to filter regular SMS, haven't gotten any unknown sender SMS yet, so don't know if it works.
Some asshat keeps sending me a text message, with the name of Brian, well in all lower case, the first one said something about money and Brian, and the one today, looked like an address. And a bogus URL I didn't click.
My name isn't Brian, and I know nobody named Brian.