In a high copper amalgam, the phase which is eliminated is:

A reaction between Cu3 Sn (ε phase) and γ2 occurs and yields Cu6Sn5  (η phase). Because of the low copper content, a majority of γ2 remains. The addition of more than 6% of copper by weight can reduce or eliminate the γ2 phase by the formation of Cu-Sn phase. Reference: PHILLIPS’ SCIENCE OF DENTAL MATERIALS, 12th ed page no 344