John Chrysostom

"And there arose a great cry: and the scribes that were of the Pharisees' part arose, and strove, saying, We find no evil in this man: but if a spirit has spoken to him, or an angel?" Why did they not plead for him before this? Do you observe, how, when the passions give way, the truth is discovered? Where is the crime, say they, if an angel has spoken to him, or a spirit? Paul gives them no handle against him.

Homily on Acts 49 ↗

Theophylact of Ohrid

Something is lacking here for the completeness of the thought. The Spirit, it is said, or an Angel suggested to him the content of his speech — it is unknown. Or this is said from the perspective of the Pharisees, and in that case the words "if a spirit or an Angel spoke to him" should be understood thus: "Behold, he speaks of the resurrection; evidently, either the Spirit or an Angel imparted to him the teaching about the resurrection."

Commentary on Acts ↗

Oecumenius

"If a spirit spoke to him." The statement can be understood in two ways. For something is lacking to complete the sense so that it may be read therefore: If a spirit or an angel spoke to him, it is unclear, he says; or as the phrase must be taken from the Pharisees: If a spirit spoke to him or an angel, instead of "Behold, I speak about the resurrection," it is evident that the word about the resurrection was taught either by the Holy Spirit or by an angel. [AMMONIUS]

Commentary on Acts ↗