Thanks for writing. Most foxgloves are biennials --- meaning they grow foliage one year, bloom the next, and then die after their seeds are mature. So it may be that your foxglove is following its natural cycle.
Or, it may be an environmental problem. Stick your finger in the potting mix; does it feel saturated or swampy? If so, your foxglove may be drowning. Have you sprayed herbicides in your yard? Herbicide drift can cause damage, as well.
---Justin, Senior Garden Editor, BHG.com