Personally I have a lock on my phone just in case I lose it and no one can access my data or files. Every time I switch my screen off it locks so I can imagine it's the same for his phone too. I don't think you've got anything to worry about. It just locks automatically if the option is enabled.

Could be force of habit. I generally assume positive intent until more evidence contrary presents itself

You said he's cheated on you previously and he's probably doing something again. The trust is gone and you need to move on

Because he does not want you snooping on his phone. Whether that is okay for your relationship is up to you.

Come on. You know. You just don't want to know. But you know you're right. There's questions in the back of your mind

Could be anything from him cheating to him trying to plan a surprise for you. Ask him, not us!

Hmmm i think you know

I think you’re right to call it a red flag. I would ask him why do you lock your phone whenever I’m around. Here’s one lame answer, oh honey, I just don’t want to be interrupted when we’re together

Is this the bf who has already cheated on you??

My phone locks automatically. My wife knows my PIN so she can unlock it whenever she wants to use it.

Because he’s up to no good

Means he has got something to hide,you need to find out why?

Duh! You know why but don't want to deal with it.

He wont hide anything from you if he's faithful

Because he has something to hide. Run

he's a cheater. kick him to the curb

He’s hiding things from you.

You should lock him out of your life

He's watching gay porn

I lock mine,purely because I'm regularly butt dial people,so I lock key screen

If it’s the guy that cheated on you before he’s doing it again.

Doesn't everyone lock their phone. I mean they lock automatically.