From what I can tell from the datasheet and the block diagram, the phase shift is relative to when it started. The output and complementary output remain 180 degrees out of phase with each other. So if you wanted two sine waves with a variable phase to each other, you could synchronize two AD9850 and alter the phase of one of them.
Here is some information on that:
I don't know enough about that chip to tell you if you can tell it the phase shift and have it start up that way. I suspect you can, it should be there somewhere. Hopefully, someone here has direct experience with it. Page 3 of the PDF above seems to indicate that this is indeed possible.
BTW, I'd read an article just a few days ago about stabilizing the output over frequency. See, you put a lowpass filter on the output so the steps from the DAC don't come through, but the signal then drops off gradually up to the cutoff frequency. I went and found the article again.
Warning: Rant follows
I read everything I found about GBW on the internet. You could have just told me that it stands for Gain BandWidth Product.
The rest I could find.
Well, I can't please everyone. I just had several people jump down my throat for not writing a book in my answer.
I don't get why people are so picky about exactly precisely how the answer is worded. The help is free, show some gratitude.
That was not entirely directed at you, I appreciate the thank you at the end of your message, and you've said nothing to me to warrant me jumping on you.
I'm just recalling how you jumped down mrburnette's throat here, calling him rude because you didn't like how he worded his attempt at helping you with the information given. I'm also stinging from the words of several other newbies (and not so newbies) calling my admittedly often terse responses rude or snarky, and calling me Mr Grumpy because I don't stroke egos.
It helps if you tell people what research you have done, or at least mention that you have done some searching and didn't find satisfactory answers. Sadly, there are a fair number of people who come here who have not done any real research, and want it all handed to them.
Some who've been around here for a very long time tend to get right to the point. You may experience Grumpy_Mike at some point. If you get angry at how he answers questions, it will be your great loss.
Keep in mind that we don't know you. We don't know how much you know, or exactly what information you are looking for. We don't know what kind of day you've had, nor do you know what kind of day anyone else here has had.