Needs to be rocked to sleep all of a sudden

Julie

My little one is 5 1/2 months and all of a sudden, he’s not good at putting himself back to sleep. Before now, he would fall asleep within 5 minutes of being put down, but now he cries and wants to be held to fall asleep, and then I have to transfer him to his crib. Is this just a phase that he will grow out of? Has this been your experience? What do I need to do to get him to put himself to sleep again?