The forgeworld guys have equipped their phoenix guard with terminator armour and power halberds, however, if we look upon the book Fulgrim of Graham Mcneil we will realize that they should be equipped with artisanal power armour and a halberd-bolter in the image of the custodes.
Let's see an extract of the book that shows Fulgrim fighting with his phoenix guard and greeting the approach of the warriors of the 1st company who are equipped diferently from the guard.
Only the warriors who had accompanied him on the Firebird fought with him, and though they fought bravely, they were being dragged down one by one, and such a rate of attrition could have only one outcome. He scanned the slopes of the valley for any sign of his battle companies. He punched the air as he saw Julius Kaesoron and the warriors of the First fighting their way through the press of slithering, screeching Laer warriors towards him.
Terminator armour gave each warrior the strength and power of a tank, and though Fulgrim had loathed these inelegant suits of armour at first sight, his heart leapt to see them now.
To make the artisanal armour I scavenged some bits from the box of the sanguinary guard, a helmet and a pauldron for each, knives, grenades and a sanguinary glave were also used.
Brother Thestis, standard bearer of the emperor's children, a character of Mcneil's book
Cloak emboidered with LEG III, the numeral of the emperor's children