Gosh, I remember the boys I went to school with and from the ages of 14-17 their one goal in life was to work out ways to get a hold of pron - whether it be magazines or videos. It was a healthy outlet for them while they were going through puberty and as far as I know none of them turned out to be sexual deviates - they are all married with kids now and who knows - maybe all their porn watching as a teen held them in good stead to become good lovers as adults? And they think they are pretty cool too if they can brag about seeing it LOL. When my DH was around 11-12yo he coveted this set of playing cards he had with the nude women on them - remember those? He would secretly take them to school and he and his mates would ogle them during lunch LMAO - picturing him doing that is just too funny for words.

However, there is a difference between teenagers exploring and just wanting to know what all the 'fuss' is about to becoming fixated with it and needing to have it kwim? I think if a big deal is made of it he is less likely to come to you with any RL issues he may have so take a 'gently gently' approach and try to bring it up in converstation without mentioning that you have gone through his phone. Teenage boys are really quite delicate creatures when you talk to them about sex (hard to imagine I know) and he is likely to get embarrassed - think American Pie - so you don't want him to completely clam up with you about it.