How to leave a group text on your iPhone.
You can leave a group text message as long as there are three other people on the thread and everyone is using an Apple device, like an iPhone, iPad, or iPod touch. You can also mute notifications for certain group text messages.
For more details please click on the link bellow:
NOTE: To leave a group text, everyone needs to be using iMessage, which is an Apple feature. Not sure if you're using iMessage or SMS/MMS? Learn the difference between iMessage and SMS/MMS.