Micah wanted his own worship equipment, in addition to the images his mother then gave him. So he made an ephod and household gods.
The ephod was a garment worn by the priests, to receive direct revelation from God. Micah’s ephod is reminiscent of Gideon’s ephod that he made and used for worship (Judges 8:27). An ephod is not for Micah to make. Micah is worshipping God in Micah’s way.
5 And the man Micah had a shrine, and he made an ephod and household gods, and ordained one of his sons, who became his priest.