Airpod A2031 Won't Connect Consistently.

I have an iphone 7 and airpod A2031 and my phone shows they are connected but sometimes when I make a call I can't hear anything and I have to manually change the audio to the airpods. Sometimes my phone will automatically set the audio to the iphone. When I make a call and if don't hear the ringing tone after a few seconds I manually change the audio to speaker and then back to airpods. This is very annoying and would like to find out how to fix this issue.