I have a new iphone6 and when my manager calls me it keeps going to voicemail?

I have checked the settings for do not disturb and they are all off. His number is the only one that the phone does this to, and the phone also doesn't even let me know that he has called?? Any help would be great
Regards Kate

Check your blocked numbers list and see if his number is listed. If so, unblock his number.

Settings - Phone - Blocked.