Yeah it won't sound great on a phone but it should at least sound good, I'll get a mix sounding nice on every other speaker system in the house but the phone poses the real challenge and that is where I will not call a mix finished until it sounds much more pleasing on a phone, I even went as far to stream straight from logic to my phone speaker to mix through that instead of bouncing down.
With the multitracks I am mixing that I can get to sound pretty nice on normal speaker setups that sound bad on the phone, is always an issue with the mix. The reference tracks I load up of the actual song I am mixing (same multitracks, same everything) will generally sound really good on the phone. Unless I can match it I would never dream of finishing that mix up, not unless I can get the mix to a place where nothing bothers me even if listening on the phone. Also, most people will actually listen to music I mix on a phone, post to facebook and probably 98% of people on there are not going to be listening on anything decent.
If your mix is not compressed right you will get a boom and really hear the compressor pumping but not in a good way. Those high mids 2-5k need to be just right and the low end can not be too hyped otherwise you will need to overbrighten those instruments in the presence range to be heard resulting in a really disgusting harsh mess on the phone. If the mix is too scooped also the phone doesn't like mixes that are done with way when the song is turned up louder.
It's tough to mix for a phone, the hardest of all. It's the one check that screws me over, but I really don't care, I would rather hurt the mix a little for a proper soundsystem to get it sounding better on the phone, no question. Nobody would even realise you are falling short of potential on a real system. But they will for damn sure notice a mix sounding like crap on a phone.
Just my thoughts on it.