The usual take on the Sphinx is that it began as a yardang, or rather, that the head (and whatever has been removed above ground level) was a yardang.
The conclusion that it wasn't originally contemplated as a sculpture is imho, but based on the evidence. The area in front of the Sphinx was quarried out as well, but there's no telling how high that was. The techniques used to move 200 ton stones out of the Sphinx enclosure may have required the final appearance, also, the body of the Sphinx (much of which is covered with small 'repairs') may have been too flawed to cut into such large blocks.
Ok, lets go with the yardang theory for a moment (although there is noting else in the area to suggest formations like a yardang).
At some point, someone had to make a decision that the protubrance looked like the head of a lion or they wouldn’t have carved the body that way. I read somewhere that the many reproductions of the Sphinx in Egypt were made after the original Sphinx was created and then unearthed.
So many theories about Egypt flying around these days with new discoveries and new technology keeping the old career Egyptologists busy with refuting them by revising their old ones.