From your Sims inventory, it is the backpack icon. I think it is next to their mood icon. Just click on the sim and it is with the career tab, happiness tab, aspiration tab, then inventory. That's where their cell phone is.
For family inventory. Like TVs and other family items, go to build mode, and click the cardboard box icon.
To move things from the inventory, Up in the left hand corner of the stack, click the button (in your inventory) that says multiple items. If you click that button, it shows all the items separately, but you can also drag and drop using that button, and that moves the whole stack.