not exactly sure what you mean...but the best way to use the phase lock is as follows..
Step 1:
Turn the F5 on and select Autotune mode.
Step 2:
Find a clear piece of ground with no metal present, using autotune or PinPoint mode. ( Note: PP mode preferred)
Step 3:
Set the threshold to a slight background hum (Note: default setting of "0" is adequate)
Step 4:
Press and hold the Phase Lock touch pad, and pump coil over clean ground (Note: pump coil from 1" off ground to 6-8 inches off ground)
Step 5:
When the phase value "settles down" to only one or numbers in variation, release the Phase Lock touch pad while still pumping the coil. Note that the audio response to the ground changed and "evened out" when you released the button, and the GB value matched the Phase value, giving you a visual AND audio Ground Balance confirmation. After balancing, you can hunt in AutoTune......or return to Disc mode.
You may be trying to Gb over a target..not sure. can you elaborate?????