Even the extra inductance added by the plane/traces from the pins to the traces to the test point, and the long ground lead on the scope will still exaggerate the spike level seen. We're trying to measure a very high frequency effect here, so standard probing techniques may be a little misleading.
I would recommend using a common HF probing technique, where the the probe tip is put right up against the PH pin, and the ground length is minimized by wrapping a length of bus wire around the scope barrel (which is grounded), and having just the end of that wire meet the GND pins of the device.
