When I'm using my OTG with my iPhone 7+ it always seems to defualt to 2.4ghz.

I have been in a few situations where I had to yank the OTG, start over, and fly over wifi becuase I was in an area with a lot of 2.4 noise and the video feed wouldn't work over 2.4ghz.

Is there a process for getting the Spark connected to the RC over 5.8ghz and the phone connected over OTG?

When I'm using the RC with OTG. It defaults to 5.8ghz. I Don't know why.

There is no current solution to this, just use wi-fi all the time

You can try:
Start drone, start RC, connect Phone via wifi.
Should be 5.8 to drone, 2.4 to phone.
Plug in otg, switch of wifi, should not affect 5.8 to drone!

but its i-connected, so .....