Thanks for clarifying this problem for me. My main point of confusion was about whether you're supposed to compare the compound's vapor pressure to its partial pressure or total system pressure when determining its phase. I initially thought that you compare vapor pressure to total pressure because to me it seemed that this is what the compound "feels." But I guess this doesn't make sense since according to the ideal gas law, each gas in a mixture behaves independently of other gases and has its own pressure.
With this being said, the partial pressures of CO2, butane, and acetylene are each 13.45 psig (28.14 psia). Based on NIST chemistry webBook, the vapor pressures for CO2, butane, and acetylene at 24oC are approximately 912 psia, 34.2 psia, and 700 psia. So it looks like all compounds in the cylinder should be in gas phase.