Funny thing is that there are quite a few android phones coming out with ESS Sabre dacs so they don't sound all that bad:
What you want is a phone with the following:
- Expandable storage
- Replaceable battery or fast charge option - with removable batteries you can use huge aftermarket batteries to get monstrous battery life.
- Strong processors, not easy to play lossless files and its taxing on weaker processors
But these days the flagship phones are doing away with storage and removable battery
If looking at phones with good audio quality by themselves
High End
- LG V10
- Meizu Pro 5 (can use headphone port as line out port via settings option)
- Sony Z5 (can natively play DSD according to sony)
Midrange
- Asus Zenfone 2 (300 USD version gets you 4GB of ram, thats insane!)
- ZTE Axon Elite (said to be audiophile quality phone but ymmv)
My recommendation would be to get a mid range phone as you get close to flagship specs at much lower prices. The 2 aforementioned midrange phones would be good but I dont know if they have removable battery.
Another solid choice would be the older Samsung Galaxy Note 4 which is nice and big, has expandable store and removable battery. A company called zero lemon makes huge batteries for them which lasts for days at a time. Depending on how much power the Mojo draws, that might be a good compromise. Most cellphones these days are ridiculously thin to begin with so stack size will be smaller relatively.
Hopefully that helped!