Up to the DM
As so many things in D&D, the phrasing is vague enough that DM adjudication is necessary.
Planar Bubble (Su): Beginning at 5th level, once per day you can create
an area around yourself that emulates the environment of your chosen
plane. This area mimics all traits of your chosen plane, including
physical traits, elemental and energy traits, alignment traits, and
magic traits. This area has a 20-foot radius and lasts as long as you
concentrate (up to a maximum of 1 hour per level) plus 1d10 rounds.
The key descriptor here is, "you can create an area around yourself", which does not specify which of the two valid interpretations you propose is the definite one.
- The area is created around yourself, as in your then-current position, and remains there if you move away from it.
- The area is created around yourself, as in around whatever position you are in for the duration of the effect.
I would judge it to be the latter, because we are dealing with a Supernatural ability I read functioning as basically your close association with another plane warping space around you, seeing as how there's no range mentioned. But your DM is the arbiter in your game, not me.