I have 50 Amp 120/208volt 3 phase service. Can I run 10, 1200wt appliances
On 2, 20amp breakers ?

Ten (10) 1200 watt appliances = 12,000 watts.
12,000 watts divided by 120 volts equals 100 amps.

One hundred (100) amps on two 20 amp circuits? No.

Maybe for 1 second, before the breaker trips.