phone (or call or ring) somebody back means return a phone call (e.g. I tried to reach you on the phone, but I was unable to get through. Please phone me back as soon as you can.)
pick something out means choose (e.g. I picked out this for you to try on.)
pick someone/ something up means to get or bring someone or something from somewhere (e.g. There was a letter on the floor. I picked it up and looked at it.)