Horizontal yellow flashy lines appear on iPhone 6 if I unplug it

I left my iPhone unlocked for about ten minutes without touching it. When I came back yellow flashy lines appeared on my screen. They only appear on the white parts of a page and do not go over images. When I went to notes it did not even have any yellow lines. I tried restarting and that did not help. I plugged my phone in to charge and I checked back ten or so minutes later and the lines were completely gone. I unplugged it and they appeared right away. I have dropped my phone in the past, I think probably 5 or 6 months ago last, I think it has been longer actually. My phone has cracks and has chips of glass coming from spots on the top of the phone, I put tape on the top corner of my phone to help with this. Does anyone have any ideas to why my phone may be acting up?

Added (1). I have only had this phone for a year and eight months

It's probably on it's last legs

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