Can Aphelios exalted buff himself?

Yes, Aphelios, Exalted can buff himself.

His ability states: "When you attach an Equipment to me, choose one that hasn't been chosen this turn — ... Buff a friendly unit."

According to Rule 702.2.a, "To Buff a Unit, a player chooses a Unit and then places a buff on it." Since Aphelios is a unit you control, he is a valid target for his own "Buff a friendly unit" ability.