Phalanx

A full-fledged phalanx (the type of phalanx Philipos and Alexander used) would be heavy on skirmishers (to counter the enemy skirmishing capabilities) light cavalry (to hunt down enemy skirmishers) hoplites (to try and create a gap in the formation of the enemy) medium cavalry (to guard the flanks, preventing any encirclement action like the one you describe) and heavy cavalry (to deliver the decisive blow in any weak point of the enemy formation) while the sarissa phalanx shall perform the pinning action!

Besides, Roman cavalry was of really poor quality. In their Greek battles they relied more on their Greek allies (yes, they defeated the Greeks with the aid of ...other Greeks) than their own cavalry.

Reliable or not your source, it still is very inaccurate!

The shield (called Hoplon hense Hoplites) covered the whole upper body as well as the comrade to the left. It was made of hard wood and covered with bronze. Often, leather aprons would hang from the lower part to protect the legs from arrows (Greeks hated arrows, considered them weapons of cowards who didn't have the guts to face opponents face to face).

Spears were usually 3 meters long and made of hard wood. They were used for thrusting not throwing. Hoplites also carried a sword that usually came into play ince the spears were broken.

The body was covered by a bronze or leather or linen "panoplia" (cuirass) and the crus by bronze grieves.

Head was covered by a bronze helmet. Varius types existed: Korinthian, Chalkidian, Illyrian etc...

The above are valid for the Classical era Hoplites. Things were different later on...