Fawq denotes “above” and taḥt “below.” When the complement is explicit, parse the normal adverbial construction; omission with a definite intended complement motivates the special building pattern.
Additional example: الْكِتَابُ فَوْقَ الطَّاوِلَةِ.
The book is above the table.
Al-kitābu: subject; fawqa: accusative place adverb and muḍāf; al-ṭāwilati: genitive complement; phrase forms the predicate relation.