1) Guess it's a matter of taste but it doesn't sound bad or wrong to me.
2) Phasers create notches. So when the notches are inserted down in the bass, it WILL suck the guts out of your signal, no differently than if someone was deliberately turning down the Bass knob on your amp. So, possible what you dislike is simply normal phaser behaviour.
3) I assume you are using a Phase 90, by your description. The one knob is Speed. Many other phasers will include multiple controls, and I was assuming them in my earlier posts. All issues of the Phase 90 include a fixed amount of feedback, replacing what would be a variable control on some other units with a single preset. Different P90 issues used different amounts of feedback in that preset, and some players prefer one issue over another for that reason. MXR/Dunlop saw a market, and has included a push-button option to select two different feedback presets on recent P90-derived products. Someissues had a wider sweep than others, as well. Typically, people like a wide sweep with more feedback when the sweepis slow, and less feedback/sweep-width when setting the speed for a faster bubbly rate. EHX addressed that in the Small Stone by having one switch that simultaneously altered speed, feedback, width, and sweep-waveshape all at once. Clever design.
4) The nicest-sounding phasers have a smoother "turnaround" - how they reverse direction at the high and low end of the sweep. The smoothness of the turnaround is a function of how well-matched the FET transistors used as control elements are. It can happen that if they are not well-matched, one or more will crap out at the extreme of a sweep, and effectively say "You guys carry on without me. I can't go any farther. I'll catch you on the way back." The phaser essentially changes from 4-stage to 3-stage or whatever, yielding a less intense effect. That can happen at either end of the sweep. The 2N5952 FETs that MXR used, and continue to use, were selected because they are very easily matched, and I gather MXR sells enough of these puppies that they have a system in place for matching large quantities of them - lord knows they've had 45 years to do so. Long story short, if you had built this phaser, I might have reason to suggest maybe better matching was needed, as a source of your complaint. But since it is a commercially-built unit, I highly doubt it is that.
5) There is a trimmer inside on the board that sets the range of the sweep. Chances are pretty good it is optimally set and glued in place. But if it isn't, you might consider tinkering with it to see if they set it to YOUR tastes at the factory. Just make note of where it started out so you can return it to that setting. Changing the setting will not fry anything. What you WILL notice is that at the extreme settings there will be no audible phasing, while in between extremes will be settings ranging from low and gurgly to higher and swirly. Myself, I like to make it a panel-mount control, but that's going too far for your needs.