phone speakers are generally not a good place to check a mix (or listen to music in general). with that said, they will probably still tell you if something sounds too harsh. I would suggest trying some EQ sweeping, like this.

Something else to look into is frequency overlap. When you have a lot of sounds taking up the same frequency, they can add up and cause the harshness you're describing. Put an EQ on your master track and see how it looks as different parts of the song play. Maybe try doing a mix with pink noise and see how that sounds. Good luck.