Thank you for using Apple Support Communities. It's my understanding you'd like to retrieve deleted text messages from your iPhone 6. I know messages can be extremely valuable. I'm happy to help.
If you created a backup while the messages were still on your iPhone, you could restore from that backup. Please keep in mind all content and settings added after the backup date will be removed. Take a look at the link below for steps to restore from a backup:
Restore your iPhone, iPad, or iPod touch from a backup
Have a fantastic day!