As with other routes, it depends which flight (there are 2 PHX-MCO) and day of the week I'm sure.

I flew PHX-MCO solo on the late afternoon nonstop on a Wednesday last month, and was quite comfortable in my exit row, as a CP
I'd hazard a guess that upgrades for a Gold would be rather difficult.

From prior experience, the best time to upgrade with miles seemed to be 8 days before the flight. When I was a lowly Silver I'd call then and it seemed they were more than happy to take my miles, before giving seats to higher preferreds for free.