Exclude photos exported from LR when importing

The photos edited and exported from LR and airdropped to the phone are JPEGs.  Unless you've changed the default camera settings on the phone, the photos imported from the phone into LR will be HEICs.

So when you import via cable from the phone, set the option Sort: File Type at the bottom center of the LR Import window. All the HEICs will be grouped together, and all the JPEGs grouped together. Select just the HEICs before starting the import.

* * 

Alternatively, install the LR Mobile app on the phone and configure it to automatically import new photos from the phone's camera roll. These will then automatically sync into LR Cloud and then down into LR Classic. In LR Classic, you can then add photos you want to see on the phone into the All Synced Photos, and they'll get automatically synced to the cloud and onto the phone in the LR Mobile app.

It will take you a bit to learn how to configure the sync settings on the phone and LR Classic, but once done, it will all happen automatically and be much faster than manually airdropping and importing.