I Need Some Honest Advice About My Hubbys Phone

Weve been married just over 2 years.My hubby has always kept his phone locked and although ive never actually tried to check it ,it actually worries me because I wonder what hes hiding.Im very open with my phone and he's free to look on it anytime and has gone through my messages before. Ive tried to tell him that it worries me as if hes hiding something-Ive even asked him if he has nothing to hide to let me look through is phone like he does with mine.Its caused us quite a few problems lately but he doesnt actually care .Originally I only realized it was locked when i needed to use his internet and he didnt want me too but eventually gave in after fiddling with it for 10 mins first-and thats when i started thinking something wasn't right.Otherwise i never would have thought about it.What Im wondering though is if im just overthinking it or does it seem like theres something wrong??