I am using Amarok as my mp3 player in KDE for many years now. I also have many playlists saved for various cases. In this guide I will describe you how you can use Amarok to sync your local collection with your Android mobile phone or tablet.
First connect your Android device to your computer via a USB cable. Choose to mount it as a disk drive and KDE will recognize it as an external device.
Now open Amarok and go to Media Sources. There you should see a Removable Media which is your Android SD card.
Right click on it and choose to Configure the USB Mass Storage Device. Tick the Music button and choose a folder in your SD card. This will be the folder were your mp3 files will be stored. Afterwards choose the filename scheme of the tracks that will be added in this device. In my case I have chosen all the files to have a format like Artist - Title.mp3 Of course you can use your own format through the many available tags and create directories as well. Finally you can choose Amarok to use automatically this device as a collection once it's plugged into your computer.
If you already have a playlist which files you want to copy to your Android open Dolphin and navigate to your desire folder in your Android device. Next simply drag and drop the files from the playlist into Dolphin's window. They will be automatically copied with the filename sheme you have selected before. Now you can see the collection you have created under Removable Media
From now on if you want to copy a track from your local collection to the Android one right click on it and select Copy to collection. In the same way you can delete a track from your Android device collection and generally manage it as you normally do with your local collections.
Once you are ready unmount your SD card and unplugged it from your computer.