Locking iPhone right as someone calls will hang up on them

I have a call/ring group, such that calls will go to my smart phone app and physical phone at the same time. If I have my phone out and lock the screen before putting the phone in my pocket, and someone just happens to call, they'll get routed to voicemail right away as if I was hanging up on them by locking my screen. I don't want customers to think I'm avoiding their calls or have to explain this to them every time it happens (it's happened a few times in the last month). Is there a way to disable this (let calls go 20 seconds before V/M always)?