This rare kanji has no clear standalone meaning. Treat its meaning as uncertain.
磈 combines 石 (stone) with 鬼 (demon/ghost), but the exact historical development is uncertain. It may have originally referred to a type of rocky or rugged terrain.
A stone (石) with a ghostly (鬼) shape: imagine a weird, rugged rock formation that looks like a demon. Its meaning is unclear, but the shape suggests something rough and stony.
For イ, picture an eerie (イ) stone demon: the ghostly rock makes you say 'ee' in fright, cueing イ.