These instructions apply to the iPhone’s built-in Messages app and not third-party tools.
That’s because organizations share supporters' numbers with each other (or even sell them).
However, this option won’t stop others who have your number.

Most of these texts tell you at the end of the message how to stop receiving them.
Tap the sender’s icon at the top.
In the confirmation pop up, tapBlock Contact.

For instance, you could miss order and appointment confirmation texts if you do.
Here’s what to do:
TapSettings.
Move theFilter Unknown Sendersslider to on/green.

TapUnknown Sendersto view all texts from numbers not in your contacts.
To completely leave the group text, there are two paths.
Change your mind and want to rejoin the group text?

you’re able to ask one of the other people in the chat to add you back.
Are spam texts a particular problem?
Check out our tips onhow to block spam texts.