Mobile devices often use capacitive touch screens which relies on the capacitive coupling with your body to work it.
You will need to incorporate materials/metal/plastics/rubber/paint that is conducive that makes contact with your skin.
You could try adapting a generic capacitive screen stylus having the rubber nub at the tip of the claw and the other end of the stylus coming back to your finger.
Also you could look at incorporating materials as previously mentioned that are available from Adafruit Industries, Unique & fun DIY electronics and kits
Something else that you may have to consider is that some devices also rely on the other hand holding it to form part of the capacitive coupling. So if you find it inaccurate/unresponsive you may have to also incorporate some conductive materials in the paw that will be holding the device while you operate it with the other paw with the adapted claw.