My sourdough starter is bubbling but not rising, suggestions?
If the starter is "bubbling nicely" then you may be already there.

Bread rises because the CO2 produced by the yeast is trapped by the protein in the dough. If you see bubbles then your starter is already producing the necessary CO2.

A starter has so much water in it that the protein doesn't trap the gas- thus you see bubbles rise to the surface. If you expect your starter to trap the gas and expand then it would have to have more protein. This isn't required for a starter to work.

You should be able to use the starter in a bread dough and that bubbling will turn into rising.