When i run the main menu of my game the fps is around 60. When playing the game fps fluctuates between 25-40. Is that acceptable? Or does a good programmer always make sure the device is getting the maximum fps possible?
A good programmer does NOT make sure the device gets the maximum FPS possible. They optimise as necessary in order to ensure that the game meets or exceeds required specifications, and then they move on 
Only you can decide what is “acceptable”. If you’re not sure, try getting some friends to test your game and see what they think. Most AAA games have variable framerates, with some experiencing noticeable slowdown when there is a lot happening on the screen. Personally, I’d say 25fps - 40fps on a mobile is pretty good, so don’t worry too much about it.