Files with "farfield" refer to the speaker:
farfield_call - driver loudspeaker during a call
farfield_fm - driver speaker in FM receivers
farfield_play - driver-speaker-mode/mp3
farfield_ring - driver-speaker-mode signal calls
farfield_rec - driver and microphone for video recording on a dictaphone.
files with "PHF_" refer to the headset (headphones):
PHF_play, PHF_2_play, PHF_3_play, PHF_4_play - when listening to music / sounds
PHF_call, PHF_2_call, PHF_3_call, PHF_4_call - if you talk
PHF_ring, PHF_2_ring, PHF_3_ring, PHF_4_ring - if a call is received
BTL_play - while the player through BT headset
handset_0_call - The Sound of conversational dynamics
Sysconn_fm - radio headphones