A writer named Stephen English wrote in his book The Army of Alexander the Great that the standard view of a "hammer and anvil" approach in regards to the phalanx holding the enemy in place is wrong, and that the Sarissa phalanx were intended to act offensively, rather than defensively, by attacking the enemy in conjunction with the Companion cavalry. He goes on to say that, once forced to fight defensively, the phalanx would easily be defeated.
What is your view of this?
I think that any characterization of the phalanx as a defensive formation is wrong. It is clearly a formation designed to overpower an enemy line and force them to rout, which, as I'm sure you know, is where the real victory in a battle comes from (and certainly the real defeat). As compared to the light infantry formations they faced, the phalanx was particularly adept at this role, esspecially in terms of line discipline. I would disagree with the assertion that 'when forced to fight defensively' it would be easily defeated. What is his evidence for this assertion? The weakness of the formation was the exposed flanks combined with difficulty in re-positioning, and the strength of the Macedonian flanks (via the cavalry) helped set it apart its Greek peers in that regard, but if any phalanx was forced to fight defensively while it's flanks were collapsing, it of course would be easily defeated. But at that point, the defeat isn't the crumpling of the phalanx, but the crumpling of whatever force was holding the flanks.
Phalanx-style tactics were revived in the late medieval / early Renaissance era as a defensive formation against cavalry charges, which probably lends to the misunderstanding of how phalanxes should be used. Late medieval cavalry tactics were very different from ancient Greek cavalry tactics, however. Ancient cavalry were probably dragoons, effectively, as mounted combat in the medieval knightly style was not feasible without the stirrup. Late medieval phalanxes were therefore deployed quite differently from ancient ones.
A medieval knight on a charger was a powerful offensive force, with a long lance, and stirrups and saddles that would keep him from being dismounted after impact. The cavalry charge therefore became the primary medieval shock tactic for shattering the cohesion of the opposing army, allowing them to be pushed off the field. The counter-tactic that eventually became widely adopted starting around 1300 was a disciplined heavy infantry with a wall of pikes, which is how phalanx tactics got revived. However, against cavalry this pike wall was very much a defensive formation. If successful, your counter-attack would quite likely be your own cavalry charge against the enemy's pike wall. Repeat back and forth until the disorder of battle caused a break in formation, allowing the cavalry to break though.
In the ancient world, cavalry did not have this shock power. Instead they were mobile archers and dragoons (mounted infantry) who could (a) rapidly respond to weaknesses in the line or counter-attack in places where the enemy was successfully breaking the line, and (b) pursue a fleeing enemy to prevent them from re-forming.
Ancient armies still needed a primary shock force to break the enemy's shield wall and force them off the field, however. Most descriptions of the phalanx have them doing just that, through the othismos - the "push", during which huge massed ranks would drive the spears forward into the enemy by sheer force. Whichever side had the weaker push would eventually collapse, and once weakened, became vulnerable to follow-on attacks by auxiliaries and cavalry.