Apply a suction cup as close as possible to the bottom edge of the phone.

If the phone's back cover is cracked, the suction cup may not stick. Try lifting it with strong tape, or superglue the suction cup in place and allow it to cure so you can proceed.

Lift on the suction cup and insert an opening pick under the rear glass.

The rear glass very fragile and can break if you use too much force or attempt to pry with metal tools.