Why is my phone acting up?

Hi all! Recently I've been having trouble with an iPhone 6. It has run fairly well for over a year now. In the past few days, there have been intermitttent problems where the screen will freeze up - nothing will move, and it won't respond to the home button - and then mover really quickly, executing all of the inputs given from the screen/home button while it was frozen (power button tends to still work but I haven't not extensive experimentation with it). Problem was slightly worse temporatily after a hard reset, but, again, resolved itself. What causes this? Is there any way I can fix this without having to open the phone and replace parts? I tend not to like working on very small and delicate componants like those in the iPhone - I've not always been known to be the most careful...

Any help is appreciated. Thanks in advance!