My boyfriend is sneaky with his phone and I’m worried. 22F 25M.

Me and my boyfriend have been together for 7 months. He doesn’t give me any suspicion that he’s cheating because he doesn’t randomly disappear at night or do other sneaky things but he acts weird with his phone. He purposely waits until I’m not looking to put in the password or wait until I’m not looking to put it in. I questioned him about it and he said he doesn’t want me to know his password because that’s his privacy and girls like to go through phones. Do you guys think this is sneaky or just privacy and a boundary?