Hello Ignat,
The frequency lock and phase lock circuits are for monitoring only, and are independent.
Were you not able to achieve phase lock by using R0x0600<7>=1?
As I said before the lock detectors are informational only.
Do you have some other means to tell if the AD9548 is locking well enough for your application? It could be that your TCXO just isn't stable enough for the lock detectors to declare that the chip is locked.
-Paul Kern