is it appropriate to spy on your ****ager’s texts

My son has an iPhone and I’m trying to find a way to monitor his texts without modifying anything on his phone because he’s fairly tech savvy so he’d be able to remove it. I was thinking about a way to spy the texts when they go over wifi. Is there a possible way to do that? f I suspected my son was into something dangerous or illegal, is it right as a parent to spy on his texts?