If Theravada doesn't posit the selflessness of phenomena, then how to interpret SN 22.95?
Piya Tan in his commentary on the lump of foam sutta, quoted Bhikkhu Bodhi's commentary below:


  This sutta is one of the most radical discourses on the empty nature
  of conditioned phenomena; its imagery (especially the similes of the
  mirage and the magical illusion) has been taken up by later Buddhist
  thinkers, most persistently by the Madhyamikas. Some of the images are
  found  elsewhere in the Pali Canon, eg at Dh 46, 170. In the context
  of early Buddhist thought, these similes have to be handled with care.
  They are not intended to suggest an illusionist view of the world but
  to show that our conceptions of the world, and of our own existence,
  are largely distorted by the processes of cognition. Just as the
  mirage and magical illusion are based on real existents — the sand of
  the desert, the magician’s appurtenances — so these false conceptions
  arise from a base that objectively exists, namely, the five
  aggregates; but when seen through a mind subject to conceptual
  distortion, the aggregates appear in a way that deviates from their
  actual nature. Instead of being seen as transient and selfless, they
  appear as substantial and as a self. (Bodhi S:B 1085 n188)


I think the above commentary discusses the Theravada view accurately. The sutta does not talk of an illusionist view of the world. It does not imply that the five aggregates are not real. It simply points towards the five aggregates as being transient and without a self.

Also, please see the Suñña Sutta, which explains this more literally, as the five aggregates being empty of a self.