You have a quart container and there's 31 ounces of stuff in it. You want to add more stuff. What do you do? Either spill out some of the existing stuff or get a larger container.
Same thing with the phone. Delete things you don't need all the time (after backing them up to a computer, cloud account or anywhere else) or get a phone with more internal ROM. Sync will stop when there's no space to put the files you're downloading.
Onetouch is a line of phones - different models have differing amounts of storage. If it's the Evolve, you have about 1.5GB available to start with (4GB, but the phone itself uses about 2.5GB). That can fill up fast.