Phone Calls and Apps

When I am using an app, phone calls go right to voicemail. I do not get any indication that I have an incoming call. What settings do I need to change? Also, where do I find the specific settings to change them? Step by step instructions would be greatly appreciated.

Thanks to anyone who can help.

Not sure what settings you would even need to change, that doesn't sound right to begin with. Apps shouldn't be affecting incoming calls. You should be getting a drop down letting you know you of an icoming call if you're in an app.