Phasis thero, the silver arrowhead or hooked copper, is a butterfly of the family Lycaenidae. It is found in South Africa.

The wingspan is 31–46 mm for males and 38–47 mm females. Adults of subspecies P. t. thero are on wing from September to November and again from March to May in two generations. Adults of subspecies P. t. cedarbergae are on wing from October to November and probably also in autumn.

The larvae feed on Rhus undulata and Melianthus major. Larvae have been found inside hollow stems of their food plant, but also in nests of Crematogaster peringueyi ants at the base of these stems.

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