The "bubble" is a part of the chip and it will most likely flake away soon. That area has lost its adhesion to the substrate and only the paint film strength is holding it in place now, but that probably won't last long.
From a spreading perspective your best course of action would be to chip away the blistered portion and then touch up the chip. The touch up paint will seal the edge of the chip and that's about the best you can do to prevent unimpeded spreading.
There's also a pretty good chance that its not going to spread (beyond what is already blistered) even if you do nothing. Touching it up is just a bit of insurance.