This may work for you and it may not. This post has an unexpected 10,000 hits.
If you haven’t heard, there is apparently a form of bad formatted text you can send to an iPhone. The text message can cause your phone to shut off or reboot.
If you get a text that says Effective Power (which is also followed by other stuff) which causes your phone to reboot or power off, go to your photos app and send any picture to whoever sent the text to you. Now open your messages and this should be gone or you can delete the message.
You may also try sending a message by Siri. If you can’t find their number, say “Siri, send ‘whatever’ to my latest text”.
Hopefully this will stop the messages and the phone problems many have reported.