The router, configured for PTP synchronization, initially starts from FREERUN state:

user@router-re0> show ptp lock-status detail

Lock Status:



Lock State  : 1 (FREERUN)

Phase offset : 0.000000000 sec

If the router receives valid PTP packets through the configured slave interface, the router goes into ACQUIRING state and further to PHASE ALIGNED. 

The master PTP device should send Announce and Sync PTP messages so the slave PTP device proceeds into ACQUIRING state. In this particular case the master PTP device (it was GM - grand master) sent only Announce massages and no Sync so the slave router remains in FREERUN state:
 

user@router-re0> show ptp statistics detail

Local Clock   Remote Clock    Role Stream   Received Transmitted

xe-1/0/0.0  01:aa:bb:00:00:0e Slave   0    961589      0

     Signalling  Announce    Sync    Delay    Error

  Rx:      0   961589      0      0      0

  Tx:      0      0      0      0      0

The issue was resolved after restarting PTP master device and Sync PTP messages can be seen in the statistics output:
 

user@router-re0> show ptp statistics detail    

Local Clock      Remote Clock       Role  Stream      Received  Transmitted

xe-1/0/0.0    01:aa:bb:00:00:01  Slave      0       1193809          165

         Signalling    Announce        Sync       Delay       Error

   Rx:            0     1193482         162         165           0

   Tx:            0           0           0         165           0 

And the router went into ACQUIRING state:
 

{master}

user@router-re0> show ptp lock-status detail 

Lock Status:


Lock State    : 3 (ACQUIRING)

Phase offset  : 0.000000000 sec