وَفِي الْأَسْمَاءِ السِّتَّةِ مُضَافَةً إِلَى يَاءِ الْمُتَكَلِّمِ، تَقُولُ: «أَخِي وَأَبِي وَحَمِي وَهَنِي» وَ«فِي» عِنْدَ الْأَكْثَرِ، وَ«فَمِي» عِنْدَ قَوْمٍ، وَ«ذُو» لَا يُضَافُ إِلَى مُضْمَرٍ أَصْلًا.
Translation: When annexing the six special nouns to the speaker’s yāʾ, the book gives akhī, abī, ḥamī and hanī; most say fī (“my mouth”) and some say famī. Under the standard rule, dhū is not annexed to a pronoun.
The form فِي here means “my mouth,” not the preposition fī (“in”). Read the rule concerning dhū alongside the exceptional poetry the author immediately mentions.