Welcome to the forum Funni,
i made my playlist on my phone ... i got the playlist file from my music app then input it into the musicbee libary
Not sure how you did this but I am assuming here that you copied the playlist file (m3u format?) from your phone to your PC, maybe using Windows Explorer.
Playlist files are text files that contain links to the music tracks based on their folder location and filename, so the playlist you copied will contain the filenames and folder locations of the music on your phone. This is almost certainly not the same filenames and folder locations that you store the music on your PC - and this is why MusicBee is saying the files are missing (because they are).
You should be able to open the playlist file in any text editor to view the paths. The exact format of this will depend on your music app and playlist file format - note that it is common to use relative rather than absolute paths.
There are probably ways to force this to work but this will depend on far too many variables for me to guess at here. It will be much, much simpler to create the playlist in MusicBee and sync that to your phone - MusicBee has all the tools to do this.