Refer to the exhibit.
There is a call flow between Phone A and Phone B. Phone B (holder) places Phone A (holdee) on hold. Which MRGL and Audio Source are played to Phone A?
a
Reference:
https://www.cisco.com/c/en/us/td/docs/voice_ip_comm/cucm/srnd/8x/moh.html
from provided reference: A will hear the MoH audio source configured for phone B (Audio-source2). However, phone A will receive this MoH audio stream from the MRGL (resource or server) configured for phone A (MRGL A). You even have it BOLD on your screenshot.