I agree. Assault his ass and profit! If they die in assault they don't get We'll Be Back.
I don't think you have played against many Necrons. 'Go for Phase Out' is not a tactical piece of advice, and you are factually incorrect about Necrons in assault.
It is like telling someone that the way to beat SMs is to 'kill all their models'. :scratchhead:
As a Necron player I find these random tactical suggestions amusing and at the same time a bit worrying. Funny because they are so wrong, and worrying because so many people believe them without actually knowing anything about it.
Lets clear up the assault thing: Necrons DO get WBB in CC, and, as most armies have RezOrbs, they even get WBB vs Power Weapons and ID attacks.
Against a Necron player who knows Necrons, and not a new player that does not know 40k rules or how the codex works, Phase Out is almost impossible in a normal game of up to 7 turns.
If your opponent is only using 20-30 Warriors in a list of 2,000pts you should be much more worried than if they are using 40-50 Warriors. 40-50 Warriors gives the Necrons a higher PO level, but it is also much easier to achieve. 20-30 Warriors is a lower PO, but there will be many things in the army that make it very hard to PO.
Sensible anti-Necron tactics:
1. Unless you know your opponent is completely rubbish, don't even bother about trying to force PO.
2. Focused fire. Target a unit at a time until it is completely gone. Necrons don't have many units to begin with, so if you kill a unit it will have a big effect. Any models that pass WBB are forced to join a different unit.
3. Don't use too many vehicles in your list. Necrons aren't as great vs AV as they used to be, but a stunned vehicle is still pretty useless so put the points into something else in the first place.
4. If you have any S9 or S10 weapons you should point them at the Monolith, try to kill it but don't bother with anything S8.
5. Avoid the C'tan if you can, it isn't really possible to tar-pit them or hurt them in CC - and as they explode when they die you would not want to hurt them in CC anyway. Poinson, Rending and Snipers work well, but remember that normal weapons must be S5+ to wound them from both shooting and in CC.
5. Target priority: Destroyers, Immortals, Monoliths/Solo D-Lords. After that attack anything you like, but remember point 2. above.
6. Try to have as high a Leadership as possible, some of the Necron powers will seriously mess you up if you fail Leadership tests, this even applies to Fearless units.
7. Play the mission. If it is an objective game then you should force the way the battle is fought by putting pressure on objectives.
There. That should be enough to start with. Lets have no more of that rubbish about going for PO and ignoring the Monolith. If you ignore the Monolith it will kill you, and good Necron players never let enough of their models get in harm's way to even get close to PO. Use your brain and not random gossip about how to beat Necrons.