Ask Mr. Smarty Plants

When we searched our Native Plant Database on the common name "Prairie Phlox," we got three results, but one of them was not native to Texas. So, your phlox is probably either Phlox pilosa (downy phlox) or Phlox pilosa ssp. pilosa (downy phlox). Ordinarily, we would recommend digging all your plants for dividing, and doing a little work on the soil in the area. Adding some compost, maybe a little fertilizer and generally fluffing up the dirt could really reinvigorate your plants. You could then break them up into clumps (they have rhizome-like roots), and replant them in the fresh new bed, and water gently but thoroughly until they start to perk up. Especially in a clumping plant like phlox, division and replanting all the plants will add to the volume of your phlox and increase its vigor. 

When we say "ordinarily" it's because we're worried about your statement that the ants "seem to have moved on."  Lots of times ants will become semi-dormant in the winter, feasting on the seeds they have been harvesting and stowing away. Also, we have had so little rain, and you didn't say if you irrigated, which could have caused them to come to the surface. And you didn't say what kinds of ants they are, maybe you haven't identified them, but we're betting no ant is going to take a shovel blade breaking through his roof without causing some trouble. We're not entomologists and we couldn't find any information on how to identify whether ants are still in residence without disturbing them. And a disturbed ant is not a happy ant. We hesitate to give you advice about something we know so little about, but would suggest you contact the Texas AgriLIFE Extension Service of Texas A&M, Travis County. Hopefully, someone there could tell you how to establish whether an ant bed is still active and how to get it to go away. 

Pictures of Phlox pilosa ssp. pilosa (downy phlox)

Phlox pilosa

Phlox pilosa