In the 277/480 VAC system the phase to neutral (and typically ground) voltage is 277 VAC. The difference phase angle makes the phase to phase voltage 480 VAC (not 277*3 = 831 VAC).

In the 120/208 VAC system the phase to neutral voltage is 120 VAC - so your right. To get 120 VAC for a wall outlet you take one phase of the three phase system. You still need a transformer to get from 277/480 to 120/208.