In the USA, is the power supplying a home a single phase? is it a single phase but two supplies lines and a neut or is it two phases that work in tandem? For a 120/240 panel Id imagine that its a matching phase but not 120/208. I work in commercial with 3 phase power primarily so I don't know too much about residential power. a couple of my coworkers and I didnt know why they called it single phase because we thought that resi had 2 phases.
I think it's more accurately called split-phase, with the two 120V lines having a phase of 180° between the two (with respect to the neutral connection).
It is not two-phase, where the voltages are 90° out-of-phase, or three-phase, where the voltages are 120° out-of-phase.
i expect the electrician will put a 120 V outlet wherever you want it
likewise a 240 V outlet - (usually kitchen for stove, laundry for dryer, garage for electric car)
Only 2 paired sockets in my Canadian home are like that at the kitchen counter so that each of the two sockets can provide up to 15A at 120V.
All other paired sockets have each pair in parallel.