Use a suction handle to pull up on the display and create a slight gap between the display and the phone's chassis.

If your display is cracked, cover it with packing tape to help the suction cup adhere and prevent glass shards from popping loose.

You may need to apply more heat if this doesn't come up. Don't be impatient, this will take time. Once you can gently insert a tool in the gap, move on to the next step.