Hi guys I am considering making an offer on the sign but wondered if this white oxidation is removable. Any help would be appreciated. Thank you!

a temporary fix is rub a little baby oil into the porcelain .. ...

And you would have to do that periodically?

that is the porcelain drying out possibly from too much exposure too the elements-
I have a couple signs that require this treatment occasionally .. ...

I had a NOS sign years ago exactly like that. I thought it was a water stain from being sandwiched wet for a long period. Never found anything to permanently fix the porcelain finish/shine. Randy is an expert so if he says wipe it occasionally, you need to plan on wiping it occasionally.
Nice sign though.

Thanks guys! I'm looking for a 6' Phillips, hoping to find one in better condition but if the price is right I may take a shot at it. Anybody know of any for sale in better shape?

The one your looking at is for sale from a seller that had 15 or more various 48" and 72" Phillips 66 DSP signs for sale recovered from a property he bought. I watched all but the last, roughest few sell on eBay, this being one of those. The white oxidation doesn't remove, and, usually looks much worse in person.

You can also use Howards Feed and Wax. However, I've never tried baby oil and Randy is much smarter than me.