Is there a research honeymoon phase?

Is this sort of phase common in research? Should I be worried about it?

It is common. Whether you should be worried about it depends on you. For example, can you imagine enjoying this even if you aren't "in love" with this. Getting a PhD, even in something you love, will be hard. There will be petty, stupid things that still require time (formatting one's thesis...). Does that strike you as a cost you're willing to bear, or do you only really see enjoying things if they're going well, there's a clear trajectory, etc.

How can I assure myself that this is not a fleeting pursuit? That I will still enjoy research in 5 years?

There's no real way to be sure this is true if for no other reason than people change in 5 years. But one way I dealt with it was to switch labs for a semester, to disambiguate if I liked all research or just the particular research I was doing. In my case, I discovered that no, I really enjoyed this thing and was not actually just enamored with the idea of research.

For what I have read you are the initial states of making research because you mention that you have done

I have gotten to read literature, submit an abstract to a conference and even work on an open source software project.

That is a very good start, but here it could happen some issues that could bring the first disputes in your newly weeding with research; these are:

• It could happen that your abstract can be rejected or even if it passes nobody assures you that your final paper would be accepted. You should get used to that, and consider that are a lot of external factors that should not discourage you; for example: personal thoughts or bias of a reviewer, low-acceptance rate of some conferences, and even maybe your work is great, but you failed to express it adequately in a research paper.
• It could happen also that you find yourself in a labyrinth without a way out when you are doing your PhD, that could bring discouragement, but also you should not let this to put you down and continue until you see a light at the end of the tunnel. In this last part your adviser has a huge role, if your communication with him or her is poor, then you can end up in a no way-out street.

Regarding your questions, even though I have pointed some important facts above that you should think about them:

Is this sort of phase common in research? Should I be worried about it?

Yes, it is common. At the beginning, you start thinking that with your research tasks your will be earning a Nobel Prize (it can be the case), but when you continue you find some obstacles that deviate you from the path you initially marked. You should not be worried about it, just enjoy the tasks that you are currently doing.

How can I assure myself that this is not a fleeting pursuit? That I will still enjoy research in 5 years?

This is a difficult one, it can happen that you will enjoy making research all your life or just it could happen that you could suffer from a burn-out and say "(f) word research" and pursue other activities. For example, I knew a very smart guy that was doing his PhD research (fully research oriented European style not the American course oriented) in a very breakthrough topic about evolution. It reached a point that his advisers and him did not manage to agree in how to end up the research; so he just drop it, published some papers as an independent researcher and not he has a business company related to construction.

Bottom line, just enjoy the research tasks in which you are now immerse, and try not to worry too much about what will happen in the future. Who knows? Maybe we have a new Turing award winner in sight!

Cheers