There's a phenomenon that the phase is randomly 0 or 180 when the frequency hopping at same target frequency with frac-N, but constant with int-N. Why? & How to keep constant with frac-N ?
Please see the following links for an explanation of this behaviour:
The feature you require is called "phase resync". It will allow the phase to stay repeatable even after a frequency change when in fractional N operation. The HMC704 does not support this feature unfortunately. I would recommended trying one of the ADF series PLLs. Perhaps the ADF41513.