My teen has been secretive with his phone lately so I need to check his text messages somehow but not sure what options work for iphones or if it’s possible without him knowing. Any advice?
Oh yes, it’s absolutely possible on iPhone and I’ve been doing it for years with my two! What worked for us was mSpy — it lets you read texts, iMessages, and even deleted ones without your teen ever knowing it’s there. Just make sure you have their Apple ID and it’s pretty straightforward to set up! 
Yeah it’s definitely harder with iPhones since Apple locks things down, but some apps like mSpy can work if you have their iCloud credentials. I looked into this stuff recently myself and honestly still figuring out how I feel about the whole thing.