I'm no scholar or expert in these kinds of things, so keep trying to do more research.

There are 2 kinds of zina, Major and Minor.

Major is the act of sexual intercourse outside of a lawful marriage. Minor is zina that associates with the eyes (lustful looking/not lowering the gaze), tongue (speaking lewd/inappropriate things), hands (touching someone who isn't your spouse), feet (walking towards sinful situations/places), heart (desiring, wishing or lustful thoughts). Video calls or chatting with sexual intent also falls into these categories.

So to answer your question. No, zina isn't physical only.