The OPL3 uses two look-up tables, each containing 256 entries. [https://g.co/kgs/Da1vEi4 Source]
This is strong evidence that the OPL chip produces the sound without any multiplications, using for 2-op frequency modulated (actually phase modulated) synthesis the formula:
out = exp(logsin(phase2 + exp(logsin(phase1) + gain1)) + gain2)