What matters is the connection(s) at the other end. If the two phase wires, with or without a neutral wire, provide power to a single 240 volt component, or to two or more 240 volt components, or to one or more components that each use both 240 and 120 volts (such as ranges), then I would call it a single circuit. If you do run a neutral, and if the three wires provide power to a collection of 120 volt components, some fed from phase A and others from phase B, then it is still one single circuit, but it is a multi-wire branch circuit. I think the only way to call this arrangement "two circuits" would be to run two neutral wires, and to keep the loads on each phase separate from the loads on the other phase.