Hi Rohan,
I do not fully understand what it is you want to do. If LFM = Linear Frequency Modulation you can easily do frequency sweeps/chirps using the DRG and RAM. The DRG should be easier to use as it doesn't require programming RAM data into the part, plus it's not limited to 1024 steps. If you need to control the amplitude on top of this, there's the OSK function which can be automatic or manual. OSK is mentioned in the datasheet on page 27.
It sounds like you wanted to program a constant FTW and then do frequency sweeping with programmed phase offsets and simultaneously control the amplitude by using polar mode. I'm not sure this is doable based on the equation you gave as phase changes can only be applied as fast as 1/4th of the DDS system clock. However the above method should be a lot easier.