What kind of phone does he have?

Okay me and my online best friend's anniversary is coming up and I'm getting him a phone case HOWEVER I do not know which iPhone he has. What's a smooth way I can figure out without straight up asking him because he'll know what I'm doing if I just ask. Any ideas?

Tell him you are interested in maybe getting a new i-phone and ask him whether he likes his and what model it is.

Ask him, out of curiosity.

Send him an article about iPhone 7 for example, and then ask him like "Really?" and he may respond "yeah" or "I don't know, I have iPhone 6", I think it might work