The prophet experiences a spiritual shift as the source of his revelation changes. Up until this stage, he received his prophecy through an angel. Now, he hears the voice of God directly, similar to the divine voice that would speak from between the cherubim [מלבי״ם]. During this encounter, the prophet stands in the inner courtyard of the Temple, while the voice reaches him from deep inside the sanctuary, the resting place of God's glory [מצודת דוד, רד״ק].
The manner in which God speaks reflects a deep sense of reverence. This is not a standard conversation. Instead, it is as if the divine voice is speaking to His own glory, or echoing through the world, and the prophet simply catches the sound and listens [רש״י, ביאור שטיינזלץ].
Beside the prophet stands a figure, agreed upon by commentators to be an accompanying angel. There are different views regarding his identity; he might be the same angel with a copper appearance seen at the beginning of the prophecy, or he could be a different messenger [רד״ק]. Out of profound respect for the Divine Presence, this angel remains outside in the courtyard and does not enter the Holy of Holies. As a result, both the prophet and the angel stand side by side, receiving the divine speech at the exact same time [מלבי״ם].