If you have a USB cable for your Android phone, this method can be the simplest and does not require an Internet connection on either the phone or the computer.
This method may not work with an iPhone as it does not use standard USB protocols for file transfers. It may be possible by using the Terminal and installing extra software, but that is currently outside the scope of this support article.
To transfer files between Endless OS and your Android phone, first connect your phone to your computer with a USB cable. Then, on your phone:
On your Endless OS computer:
When you're finished, select the ⏏️ icon next to your phone's name in the sidebar to "Unmount" it.
This method requires a Google account, and the same account must be set up on your phone and Endless OS via Online Accounts.
Since Endless OS offers Google Drive integration, it can be a great solution for sharing files between your phone and computer, assuming both have an Internet connection.
Even though you can see Google Drive files in the Files app, they are not stored on your computer for offline access unless you copy them to somewhere else on your computer, e.g. the Documents folder on the sidebar.
If you're using an iPhone and have an Internet connection on it and your Endless OS computer, you can transfer files using iCloud.
Refer to Apple's support articles: