Numbering in phenolphthalein versus ascorbic acid According to Wikipedia, the recommended IUPAC name for phenolphthalein is 3,3-bis(4-hydroxyphenyl)-2-benzofuran-1(3⁠H)-one, and for ascorbic acid is (5⁠R)-5-[(1⁠S)-1,2-dihydroxyethyl]-3,4-dihydroxyfuran-2(5⁠H)-one.

Why does the numbering in phenolphthalein start from the $\ce{O}$ atom next carbon atom, while in ascorbic acid it starts on the $\ce{O}$ atom? If we want to prioritize the keto group, why doesn't the numbering start on the carbonyl carbon? And other groups attached to the furan on both molecules don't seem prioritize any of the 2 counting.
The subsituents do not take the highest priority here, rather, it is the parent molecule that determines the numbering. According IUPAC's organic chemistry book for nomenclature, the Blue Book, for heteromonocyclic components fused to a benzene ring:


  P-25.2.2.4 (...) The presence of a single heteroatom determines the numbering in a monocyclic compound; the heteroatom has the locant ‘1’.


This gives the following numbering for the isomers of benzofuran:



The parent molecule of ascorbic acid is a furan ring, for which the numbering is dictated by skeletal replacement ('a') nomenclature:


  P-15.4.1.2 For naming and numbering purposes, the following decreasing order of seniority is followed: $\ce{F}$ > $\ce{Cl}$ > $\ce{Br}$ > $\ce{I}$ > $\ce{At}$ > $\ce{O}$ > $\ce{S}$ > $\ce{Se}$ > $\ce{Te}$ > $\ce{Po}$ > $\ce{N}$ > $\ce{P}$ > $\ce{As}$ > $\ce{Sb}$ > $\ce{Bi}$ > $\ce{C}$ > $\ce{Si}$ > $\ce{Ge}$ > $\ce{Sn}$ > $\ce{Pb}$ > $\ce{B}$ > $\ce{Al}$ > $\ce{Ga}$ > $\ce{In}$ > $\ce{Tl}$.