You cannot see blocked messages on iphone but you can recover your deleted messages with the help of iTunes backup and for that you must follow these steps:-
1. The intial thing that you need to do is to connect your iPhone to a computer via a suitable cable.
2. Now open iTunes on your computer.
3. Then click on the iPhone icon located at the top of the screen and select summary from the menu.
4. Now choose the option to backup your data on your computer and then finally click on restore.