RIAA phono eq is how LP (long playing) records were achieved.
During recording, the bass signals are cut, thus smaller/narrower grooves are needed/made by the cutter. Move narrow grooves = Long Playing.
At the same time, the highs are boosted, enlarging the grooves so the same size stylus can track the narrower bass grooves and the wider treble grooves.
It also separates the highs further from surface noise frequencies, like Dolby did later for tapes.
During recording, the bass signals are cut, thus smaller/narrower grooves are needed/made by the cutter. Move narrow grooves = Long Playing.
At the same time, the highs are boosted, enlarging the grooves so the same size stylus can track the narrower bass grooves and the wider treble grooves.
It also separates the highs further from surface noise frequencies, like Dolby did later for tapes.