he called / he prayed / he supplicated
Defective verb (nāqiṣ). Past: دَعَا, Present: يَدْعُو. Related: دُعَاءٌ (supplication), دَعْوَةٌ (call/invitation), دَاعٍ (caller). Also means 'to invite' (daʿwah).
This is one of the most intimate verses in the Quran - notably, God responds directly without the Prophet as intermediary, emphasizing the directness of the relationship between God and the worshipper.