assistance needed with unwanted texts

Lately I've been getting a lot of texts from strangers peddling sex in some fashion. I can't believe that anyone would be stupid enough to respond but that is another issue. I have an Apple phone. How do I stop them? There is no number attached to them so I can't simply block the number. There is sometimes a url noted but I'm not going through all that trouble since I get a lot of these from different people. It's annoying as hell.

Can I simply set up my phone to receive texts from only certain numbers? thanks!