I know exactly where you are coming from, and it is a huge bummer  when you mix, export and upload a track onto your phone or device only to find it is super weak

Something I learned from a Soundprank (Colin Fischer) mixing tutorial was that he uses the technique of putting utilities on all of his bus channels. Then goes in and turns them down and creates his starting point with his kick around -18db.

I am sure some will read this and say wtf?! However after having tried it, it def works.

I do the same now and do my mix down with my interface maxed out while still keeping my track at a level I can have a conversation at. On my master chain I first have a utility and then turn it up on my master. I follow that with my master chain to simulate a mastered effect, and tweak where needed. Releasing music as a bedroom producer, this technique really has helped me translate my mixes onto all systems, not just my studio monitors and headphones, but laptops and Bluetooth speakers as well.

Hope this helped, good luck!

Digging into your eq's to create some space might work. If it really sounds terrible you might have to go back to your sound design. You could try side chaining your tracks that you want on the edges of your stereo field with your track you want in the middle to let that come through first and then adding some ambience to the outer edges.