Assuming this is an Android phone, you need to make sure you have the appropriate mtp libraries installed on your Mint PC, to support MTP (media transfer protocol).
Then you should be able to use your file manager to drag and drop files from your PC to your phone, or vice-versa!
Use apt search libmtp —names-only
and that should list any packages and their installation status.
If you don’t have libmtp installed, then install it using sudo apt install {nameOfPackage}
where {nameOfPackage} is the exact name of the libmtp package.
If memory serves there are a few mtp packages. A common package, a runtime package. And I think there’s also libmtp-tools, which I believe has some command line tools for dealing with mtp transfers.
I don’t know if libmtp is included in Mint’s default installation. But I know it’s not installed by default in Debian.
Either way - check to see if you have the appropriate mtp libraries installed and install them if there are any missing.
Then you should be able to plug in your phone and just drag and drop files in your file manager.