Is there an App that will allow transferring of photos (or files) between a PC and an iPhone 6S using WiFi so that I don't have to constantly keep removing the wall plug from the cable and plugging the cable into the iPhone and PC?
There are a few services/cloud storage option and apps you can use. One of them would be iCloud, if you download it to your computer. Afaik, you can add images to iCloud on your computer, and they will sync to your other devices connected to iCloud. 5 GB of iCloud storage are free, if you need more space, you'll have to upgrade.
If you have a Gmail account, you can use Google Drive for files and photos, or Google Photos for pictures only. There's an app for both. You start with 15 GB of free storage, and it's possible to get a bit more.
Microsoft's OneDrive has an iOS app as well, and it can sync files and pictures. In July, they'll reduce their free storage space to 5 GB, so if that's not enough for you, better not use it.