Not sure I would call Phoenix and Rockwell "lenders" - The connections with IRP and others implicate more of a relationship than that. I suggest you read the links and connections nodummy has found and posted here.
I would not consider these guys lenders - neither Phoenix nor Rockwell "loaned" MYDX anything, they are settling many supposed "debts" of MYDX which research shows to be nebulous, at best.
Perhaps even straight up concocted "debt" such as this 1 million dollar contract with a Lynx Consulting Group LTD using a registered business address of 4301 Road Town, Tortola BVI - a well known money laundering drop box as identified in the Panama Papers, Offshore Leaks, and by the ICIJ International Consortium of Investigative Journalists.
The matter is not about MYDX "lenders". And I find no evidence of either Phoenix or Rockwell being registered broker dealers, but welcome any evidence to the contrary.