I never found anything definitive that states upstream PhyR does not exist for ADSL2/2+. Perhaps it is just not enabled for your line.
I can speculate about the reasons why the designers didn't do upstream retransmission for ADSL2/2+:
- The primary motivation for retransmission was for the delivery of IPTV, a downstream only service.
- The ADSL2/2+ upstream uses lower frequencies than the downstream, which have lower attenuation and maybe suffers less from interference anyway. This is unlike the VDSL2 upstream, where most of the upstream bandwidth comes from high frequency bands.