We have found this method problematic with a Samsung S8. Initially, when you plug in your phone, it does not come up in your finder window as a new drive.
To get it to register you can try and download Android File transfer.
https://www.android.com/filetransfer/
When you plug your phone in you have to tell it that it is being used as a Disc drive, not for charging. In theory you will get a window for Android File manager then you open a new finder window on the Mac and drag over your content. I find the Android file manager window keeps disappearing. It's a clunky process and not recommended.