Now this man Micah had a shrine, and he ORDAINED one of his sons as his priest

[TonyChanYT]

Exodus 28:

3 Tell all the skilled workers to whom I have given wisdom in such matters that they are to make garments for Aaron, for his consecration, so he may serve me as priest. 4 These are the garments they are to make: a breastpiece, an ephod, a robe, a woven tunic, a turban and a sash. They are to make these sacred garments for your brother Aaron and his sons, so they may serve me as priests.

Originally, the ephod was designed for the high priests only.

Judges 17:

1 Now a man named Micah from the hill country of Ephraim.

5 Now this man Micah had a shrine, and he made an ephod and some household idols, and ordained one of his sons as his priest. 6 In those days there was no king in Israel; everyone did what was right in his own eyes.

Was Micah a high priest?

I don't think Micah was a high priest, even though he might think he was. He did what was right in his own eyes. I don't even think that he was a Levite. By chance, a real Levite did come by his way.

9“Where are you from?” Micah asked him.
“I am a Levite from Bethlehem in Judah,” he replied, “and I am on my way to settle wherever I can find a place.”
10“Stay with me,” Micah said to him, “and be my father and priest, and I will give you ten shekels of silverd per year, a suit of clothes, and your provisions.”
So the Levite went in 11and agreed to stay with him, and the young man became like a son to Micah.
12Micah ordained the Levite, and the young man became his priest and lived in his house. 13Then Micah said, “Now I know that the LORD will be good to me, because a Levite has become my priest.”

Now, this real Levite replaced his son as a priest. Micah might see himself as some sort of high priest. By hiring a Levite, Micah puffed himself up as a false high priest in the false religious worship of idols.