You're 99% of the way there.
The "high level" in/outs are used with speaker connections (if your receiver didn't have an LFE output) and it sound's like for your application, you won't use those at all.
The RCA connection goes to your receiver just as you've reasoned but since your receiver has a left LFE and a right LFE, it's designed for two subwoofers. Since you only have one, check to see if there is a receiver menu which selects something like "single woofer use". It's quite possible that the receiver sends identical audio to both LFE outputs, in which case you're fine as is.
As you surmised, any decent audio cable will work for the sub line. You only need a single line though you can use a red/white cable and just use one side (like you described). Check with Monoprice if you want a single line cable.
The phasing switch (0 or 180 degrees) should be set so your subwoofer reinforces low frequencies. Just play something with really low frequencies and switch it back and forth. Leave it at the setting which give the loudest room fill for the lows. If your main receiver is directing low frequencies to just your sub, the switch position won't make much difference. In that case leave it at 0 degrees.
Last edited by RBTO; 01-19-2014 at 03:11 PM..