"Phantom power" is a term that goes with balanced, XLR connections, which your camera doesn't have. The equivalent for unbalanced, 3.5mm connections is called "Plug-in power". It's worth knowing that these two systems (balanced and unbalanced) are very different, and really not compatible; for example the voltages they use are very different. So for your camera, make sure to get an unbalanced mic with a 3.5mm plug.
Most cameras supply plug-in power. Looking at the manual for the r800, it seems that it does not, which is a little unusual. So you need a mic with a built-in battery. The manual actually says this.
Good news, there are such mics. I haven't used any of them myself, so I really can't give any recommendation. But for example the Rode VideoMic Pro and Deity V-Mic D4 say they take batteries.
If you want to know more about mic connections, I made a video about that: https://moonblink.info/FieldRecording/content/course#Connections
