Hi Guys does anyone know how do I go about parent or constraint a phone to a metahuman? Thank you so much in advance!
Quite simple. Add the item to the sequencer, then on the items track in sequencer press the “+track” button (or whatever button appears on its track layer - I’m not at my computer lol). Then find the “attach” option. Choose your BP_JOHN or whatever your metahumans name is. Then choose where to attach 
You can attach in sequencer but best to attach to the hand or you can go into the skeleton and make a sock in the hand to attach to.