Wikipedia says that 3G cuts off at 3400 Hz (by filtering). It also says 8 kHz sampling frequency, which should mean a hard limit of 4 kHz for reproducing sound.
As @dos says, VoLTE allows much higher quality codecs, so for a guaranteed apples-to-apples comparison, you would want to disable VoLTE on the Samsung phone (and one way of achieving that may be to disable 4G).