Hey, thanks for the reply! I'm on a OnePlus 3T but the thing is, just last update I had an equalizer and would always switch between the metal and hip hop presets. That's why I'm super confused as to where it went!
Didn't the phone recently receive an OTA firmware update? This reddit thread indicates that there were changes with the update to android nougat.
EDIT: I also came across this which indicates that "The equalizer can be found under audio settings (last entry in the audio settings screen). It only works with headphones.". Bottom line is that it's an OS issue. Spotify will display the equalizer option if an equalizer is available in the system.