In acting, or in speaking, you may have heard the phrase, "phoning it in". It basically means that rather than giving it your all in doing something or performing, you simply go through the motions, and phone it in. I've heard of lots of performers that do this, actors, singers, etc. They kind of just go through the motions without adding any kind of personal connection.
This usually occurs with people who are most celebrated in their own mind. They consider themselves to be better than they are, and because they are so good at what they do, they don't require any additional training, nor do they need to put any effort into what they do. It's just "star power" really.
It can also occur when the performer has led himself to believe that he is undervalued or placed in a role that is "beneath him". For example, I was with people in college who were incredibly gifted actors/dancers and in some shows they were cast as the "chorus". They were still really good – but maybe put less effort into it.
I think we can be guilty of this in life every day. We kind of "phone in" who we are. We make ourselves out to be more important than we are (pride) and we become complacent in our walk with Jesus. We are so good, we know so much already, that we don't need to pray today. We don't need to read God's Word today. Or maybe, we forget how valuable we are to Jesus. We forget that he sacrificed himself for us. We are worth the price of Jesus' death on a cross, and we walk around like we aren't worth that much. Why bother put in the effort?
The difference is this. You can't "phone in" your identity. It's who you are. If you are a child of God, then you are a child of God. Live like the child of God. Walk humbly in grace, but confident in who He is. Don't "phone it in". Every day, live for the one who died and lives again. Live with the purpose He called you to. Be intentional. We are called to be complete in Him. That doesn't happen by accident. It requires a renewing of the mind, a redemption of the heart.