Ad hoc work detracting from PhD project Setting
I am a graduate student in a quant/informatics group (size = 2 people: my advisor and I) housed within a larger academic group that do wet laboratory/bench research. I have my own project independent of those in the larger bench research group.

Problem
We often get requests from the bench researchers for some data analysis. My advisor has been passing all these ad hoc requests to me and I do duly comply.

Anticipated consequence
If the current pace of requests continues, I think that my PhD project will suffer.

What actions should I take and why?
Step 1: Gather data. For an appropriate period of time, keep a record of who asks for what task and how long each task takes to do. If you have comparable control data from before the requests started flooding in, track progress on your own project also, so that you can demonstrate the damage to your own work.

Step 2: Bring the problem to your advisor. Show your advisor the data. Explain what you need in terms of time: X amount of time for your own work per Y work period. Ask your advisor how best to make that happen (do bring ideas if you have them, but be open to things you haven't thought of).

Step 3: With your advisor's support, bring the problem to the rest of the research group. You should do this with proposed solution(s) in hand (one common Organization Hack is to bring two or three possible solutions, any of which would content you, in order to limit the apparent options to wins for you).

Derailment is possible here, especially if your advisor is unsympathetic, but a calm and data-driven approach is likeliest to achieve your aim.