txnoo7, I would be just as frustrated with being bombarded with ads after every call. We are here to help out. Typically, this type of behavior is caused by an app that is programmed to display an ad as an overlay on that screen. When you first activated your phone, and added your Gmail account details, did you automatically restore content such as apps on to your new phone?
If you run your phone through Safe Mode, do the ads go away?
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UPDATE: I found out that the default phone app is set up out-of-the-box to load a notepad after hanging up from a call, so the user can enter notes about the call. The ads are actually within this notepad app. You can turn this "feature" off in the Phone app settings. I just didn't dig deep enough!