Phillip might have not change the shield. The shield the Macedonian hoplites used was introduced between 413 and 400 by the reforms of Archelaos. This sheild was 60-75cm and Phillips seems to have changed the shield grip, so that the palm of the shield-arm was at the edge of the rim. This means that the sarissa could be hold with two hands.

Something like this. Perhaps the shield was a little smaller than that.