I need your help with my Anker SoundBuds In-Ear Sport

I recently bought an Anker SoundBuds In-Ear Sport but I have a problem with them. When I connect my iphone 6 (iOS 10.2.1) there is too much interference and it sounds really really bad even if the phone is very close. I tried to disconnect the Wi-Fi and put the phone in airplane mode only with bluetooth on and the problem continues. I’ve also tried with an old iPhone 5 (iOs 9.3.1) that I have and it works perfectly without any interference. Why is that?

Could someone please help me with this problem?

What do you mean by interference. does it disconnect from your phone? does it have static?