- Phalanx makes you take a dangerous terrain test, but only up to as many tests as models with phalanx. - A dangerous terrain test makes you roll one die, or as many as your tough value.
So because we have 10 models, we need to take 10 tests. If you added a hero with Tough(3) to the unit, then you would take 13 tests. If there were only 5 models with phalanx, then we would only take 5 tests.