The Sphinx is not the head of a Pharaoh and the body of a lion. It's actually the body of Anubis (the Greek name for a jackal-headed god).
When the head of the Anubis (the Sphinx) was destroyed with only the neck remaining, the neck stump was carved into a human head with the face of Pharaoh Amenemhat II.
The God Anubis
Olivia & Robert Temple interviewed by Philip Gardiner.
Olivia & Robert Temple Website: http://www.sphinxmystery.info/