Hello jjaney,
Thanks for reaching out to us for support. It’s never fun when the screen orientation is off when you're sending text messages, and we are going to do everything we can to help you. When you have a free moment, can you please tell us when you first encountered this issue and if you have made any changes to the settings on your iPhone? Also, can you please tell us the version of iOS you are currently running on your device?
Find the software version on your iPhone, iPad, or iPod
If you find that you’re running a dated version of iOS, please use the link below to update your device, followed by testing, and let us know if you’re still noticing the same behavior.
Update your iPhone, iPad, or iPod touch
Thanks for using the Apple Support Communities.
Cheers!