Where are those logs you provided from? Which device did those come from? Are you able to take a packet capture (EPC is fine) on the edge node interface where this IP phone is connected and share those?   

Hello, the certificate exchange process occurs during trust establishment between ISE & DNA Center when the integration is executed. This process is automated during this integration.

You would need to purchase either DNA-Essentials or DNA-Advantage licenses for the network devices. Take a look at the following screenshot, it lists which DNA features are available per license level:    

What username are you using to login with?

Unfortunately, no there is not. If you have the access points placed on the floor map in Prime Infrastructure, you can export that data from Prime Infrastructure into Cisco DNA Center. If this is not an option, the only way for you to be able to tell...