Q: Messages deleted

Hello ri.an,

Thank you for being part of the Apple Community!

Reading your post, it is my understanding that your iPhone 6 is missing messages.  I know how important those messages are.  I use messages to stay in touch with a lot of people.

The best way to retrieve those missing messages is going to be to restore from a backup that still has them.  You do mention that you backed up the iPhone after the messages went missing.  There are actually two different ways to backup your iPhone.  It can be backed up using iCloud or iTunes.  The key to whether you will be able to get them back is if you use both methods.  If you used iTunes to back up after the messages were missing, which it sounds like from your post, you can try to restore from iCloud by using the steps outlined in this article:

iCloud: Restore or set up your iOS device from iCloud

If you do not have an iCloud backup available, you may have an older backup in iTunes you can choose.  Follow the instructions on this page to restore from iTunes:

Restore your iPhone, iPad, or iPod touch from a backup

You also mention that you are having issues with restoring from a backup due to not having enough space on the iPhone.  In this case, you may need to erase the iPhone and then restore it from the backup.

How to erase your iOS device and then set it up as a new device or restore it from backups

Have a great day!