What is an idiom/phrase for achieving just the tip of the iceberg?
Winning the battle but that is just the beginning of the long war. The achiever is aware that this is just the end of the beginning, nothing more.
This project is very big and complicated, and so far I have only scratched the surface.
to deal with only a very small part of a subject or a problem.
Now this is not the end. It is not even the beginning of the end. But it is, perhaps,
the end of the beginning.
Wikipedia says the address came after the Battle of el Alamein, but for some reason I keep thinking it was referring to another battle...
As you may recall, the 1942-3 Battle for the Libyan desert went back and forth a couple or few times...the final battle ended Rommel's domination in Northern Africa; he was subsequently recalled.
This was widely cheered by British people (and indeed by much of the free world), and the quote from Churchill's speech comes down to us through history to become the well-known phrase.
Compare that with Gen. Westmoreland's
light at the end of the tunnel
Having your work cut out for you could work here. The phrase was originally meant to evoke a tailor having fabric cut out in preparation for the harder task of making a garment, so it carries a connotation of the easy part being finished and the hard part being about to begin.