Your iPhone has an issue that you can't notice in your daily use ? Well, so your iPhone doesn't have an issue
How many threads on this forum where people perfectly happy of his/hers iDevice found out to have "a problem" just because told so by someone ? I'm speaking about most of the "discoloration" , "image retention" and "backlighting bleed" threads you can find here ...
I'm not saying there isn't flickering problem on some unit, on the contrary I'm sure there are defective units, I'm just saying it's not a problem for most of the iPhones ....
----------
Not completely sure, but I think refresh rate on a phone is not set by software.