The phone AC current jumps to 90 VAC
Current is measured in Amperes, Potential difference in Volts.
why don't AC currents from 'LV' phone affect adjacent speaker wires?
Magnetic flux is directly proportional to current.
The current flowing when the phone rings is small, very little magnetic flux.
Speakers are low impedance devices, inducing enough curreent into a low impedance circuit to be audible is very difficult.