My boyfriend has a lock code on his phone. I just don't understand.What does that mean?

I mean when he gets a text or call he'll sometimes look at it, reject the calls and text or let it ring. Honest Advice?
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But the thing is I've ask for his password once to his phone then after that he change it. Is that suspicious?
My boyfriend has a lock code on his phone. I just don't understand.What does that mean?
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