Delete and Report as Junk

If iCloud is backing up your phone, you will need to temporary disable the iCloud backup. Then you'll be able to swipe the messages to the left to get an option to delete them.

This is an annoying new feature. I hit the delete and report junk by mistake on an important number. What will happen? Will that number get blocked? If so how can I unblock it?

How to Unblock a Number on iPhone (howtogeek.com)