The top-left flex cable is the culprit for the added difficulty of fully separating the two pieces. But, since the adhesive is relatively small (see 2nd photo), by lifting the connector at a 90 degree angle away from the phone at a slow, steady pace, it should disconnect without damaging either cable

Notice how much adhesive is holding the ribbon cable against the phone, but do not judge its effect by its size, or you may lose some critical phone functions!

This is the flex cable that is likely to tear if you are not careful when removing the connectors from the adhesive. I believe it is the proximity sensor cable, which turns the screen off when you have your face close to the phone (during a phone call)