The crosstalk of 10 years ago returned. The mane cause was narrowed down to sharing the same package with the microphone follower & speaker follower. Taking out the speaker follower ended most of the crosstalk. The microphone follower proved essential to get enough microphone gain. A small amount of crosstalk remaned when the phone volume was maximum. Lowering the phone volume halfway got rid of it.
After taking out the microphone follower, taking out the phantom power, having the microphone pass directly to the phone, the same amount of crosstalk existed. Changing the speaker gain on the circuit had no effect. Only lowering the phone volume ever got rid of it. The cause was believed to be in the phone itself. There is enough gain in the headset circuit to make up for a lower phone volume.
The amount of rework & flux is quite a mess.