Phasing "issues" are not all bad. It is the time of arrival difference to our ears which creates a sense of size and depth. Recording with one microphone is fine, but you might want to add some delays or reverb (again, time-of-arrival differences) to give your guitar a sense of size and space, otherwise it might just sound like a guitar in a bedroom...
As to placement, there are many options for acoustic guitar. Three of the popular ones are: 1) mic pointed at the 12th to 14th fret (and a distance from the instrument of a few inches to 1 foot or two); 2) Placed about 6" to 1' over the right shoulder (shoulder of the strumming hand), facing down towards the bridge. 3) 1 to 2' away from the lower bout, aiming at the bridge. All these techniques have "a sound" and advantages/disadvantages. And they may require a bit of EQ to make the sound optimum.
Pardon me if this sound preachy as I don't mean it that way: A guitar is an "acoustic" instrument and as such the sound needs space to bloom. Be careful how close the mic is and don't record in a small room.