Why does my boyfriend always lock his iphone and keep it face down?

Why does my boyfriend always lock his iphone and keep it face down?

He's afraid that you will see something that is private (often another girl's messages)

So you don't see the messages from his other girlfriend.

I do that cause it's just habit. He might be hiding something, but I would assume that's just how he always puts his phone down. Who doesn't lock their phone any who?